Perspectives on Variations in
the Upper End of the IMF
Clarke
The maximum stellar mass in
clusters: evidence from observations and hydrodynamical simulations
Weidner
The galaxy-wide IMF - from star
clusters to galaxies
10:50 - 11:10 AM
Coffee Break
11:10 - 12:40 PM
Session I Continued (moderator: Oey)
Massey
What the Stellar Content of OB
Associations Tell Us (and Not) About the Slope of the IMF and Upper Mass
Cutoffs
Selman
Around the Tarantula and into
the Arches: a Salpeter IMF in the field and in clusters.
Comeron
RCW 108: Massive star formation
in a nearby troubled environment
12:40 - 2:30 PM
Lunch
2:30 - 4:00 PM
Session II (moderator: Oey)
Stolte
Clusters near the center of the
Galaxy - how weird is their IMF?
Johnston
Probing the origin of the IMF in
regions of massive star formation
Lu
Mass Functions for Young
Starburst Clusters in Different Milky Way Environments
4:00 - 4:30 PM
Coffee Break
4:30 - 5:30 PM
Session II Continued (moderator: Krumholz)
Oey
OB Stars in Stochastic Regimes
Vink
How massive is the most massive
star?
Tuesday, June, 22nd
7:30 - 9:00 AM
Breakfast
9:00 - 10:40 AM
Session III (moderator: Ferguson)
Krumholz
How Does Radiation Feedback
Affect Fragmentation and the IMF?
Smith
Can environmental conditions
affect the upper end of the IMF?
Scoville
Determining the Upper End
Requires Knowing the Lower End
Hsu, Urban
Poster summaries
10:40 - 11:00 AM
Coffee Break
11:00 - 12:40 PM
Session III Continued (moderator: Ferguson)
Corbelli
The Cluster Birthline and the
formation of stellar clusters in M33
Calzetti
A New Approach to Measuring the
Stellar IMF
Cerviño
From CMDs to Integrated
properties: Probabilistic synthesis models
Wofford,
Kim, Fumagalli
Poster summaries
12:40 - 12:50 PM
Conference Group Photo
12:50 - 2:30 PM
Lunch
2:30 – 4:00 PM
Session IV (moderator: Ferguson)
Zinnecker
The Chances of Massive Star
Collisions in the Center of the R136 Cluster Core
Whitmore
Luminous Stars in Galaxies
Beyond 3 Mpc
Weisz
Constraints on the Field Star
IMF from Resolved Stellar Populations based Star Formation Histories
5:45 – 8:00 PM
Sunset Jeep Tour (meet at Village Terrace)
Wednesday, June, 23rd
7:30 – 9:00 AM
Breakfast
9:00 - 10:30 AM
Session V (moderator: Schiminovich)
Lee
UV/H-alpha Turmoil
Meurer
Upper-End IMF Variations Deduced
From HI Selected Galaxies
Boselli
High Mass Star Formation in
Normal Late-Type Galaxies: Observational Constraints to the IMF
10:30 - 11:00 AM
Coffee Break
11:00 - 12:40 PM
Session V Continued (moderator: Schiminovich)
Thilker
The role of extended ultraviolet
disk (XUV-disk) galaxies in the IMF controversy
Eldridge
How star-formation rate
indicators vary with the IMF and how it is sampled.
Johnson
Fitting the UV through IR SED of
Galaxies in the Local Volume
Wyder,
Donovan-Meyer, Zhang
Poster summaries
12:40 - 2:30 PM
Lunch
2:30 - 4:00 PM
Session VI (moderator: Gallagher)
Hoversten
Evidence for IMF Variations from
the Integrated Light of SDSS Galaxies
Dabringhausen
Top-heavy IMFs in ultra-compact
dwarf galaxies?
Pflamm-Altenburg
Applications of the IGIMF-theory
4:00 - 4:30 PM
Coffee Break
4:30 - 6:00 PM
Session VI Continued (moderator: Gallagher)
Jungwiert
N-body simulations of disk
galaxies with long-term stellar mass-loss within the IGIMF framework
Calura
The Role of the IGIMF in the
chemical evolution of the solar neighbourhood
Zahid
Poster summary
Kroupa
Some implications of the
variable galaxy-wide IMF
Thursday, June, 24th
7:30 - 9:00 AM
Breakfast
9:00 - 10:30 AM
Session VII (moderator: Gallagher)
Madore
What Is This Thing Called the
Schmidt Law?
Gunawardhana
The dependence of the stellar
initial mass function on the galaxy star formation rate
Leitherer
Constraints on the Upper IMF
from Ultraviolet Spectral Lines
10:30 - 11:00 AM
Coffee Break
11:00 - 12:30 AM
Session VII Continued (moderator: Scoville)
Neill
Measuring the Upper End of the
IMF with Supernovae
Cooke
Type IIn supernova detections in
z ~ 2 Lyman break galaxies: Probing the IMF directly
Le Tiran
The turbulent ISM of galaxies
about 10 Gyrs ago: an impact on their IMF?
12:30 - 2:30 PM
Lunch
2:30 - 4:05 PM
Session VIII (moderator: Scoville)
Hayward
The IMF in z~2 Starbursts:
Evidence for Minimal Variations from LocalMass Functions
Wilkins
The Effect of an Evolving IMF on
the Cosmic Star Formation History
Reddy
Reconciling the Star Formation
and Stellar Mass Density Histories
Watson, Giavalisco
Poster summaries
4:05 - 4:30 PM
Coffee Break
4:30 - 5:30 PM
Session VII Continued (moderator: Scoville)
Davé
The Odd Meanderings of the IMF
Across Cosmic Time
Murphy
The Possibility of Identifying
Variations to the IMF at High-z Through Deep Radio Surveys
7:00 - 9:00 PM
Banquet (Village Terrace)
Friday, June, 25th
9:00 - 11:00 AM
Brunch(Agave room)
Ferguson, Gallagher, Scoville,
Krumholz, Calzetti
Review Panel / Group Discussion
11:15 AM
Adjourn Workshop
Poster Presentations
Donovan Meyer
Star Formation in the Outskirts
of Early Type Galaxies
Fumagalli
SLUG: A new way to
Stochastically Light Up Galaxies
Giavalisco
Star Formation in Massive
Galaxies at Redshift 2<4
Hsu
Competitive Accretion in Sheet
Geometry and the Stellar IMF
Kim
Study of Resolved Stellar
Populations in M83 using HST/WFC3 Early Release Science Data
Urban
Studying the effect of radiation
and dust-gas energetics on clustered star formation
Watson
Testing the Star Formation Law
in Bulgeless Disk Galaxies
Wofford
The Massive Star Initial Mass
Function of Circumnuclear Clusters in M83
Wyder
H-alpha and UV imaging of XUV
disks and LSB galaxies
Zahid
The MZ and LZ relation from
DEEP2 at z ~ 0.8
Zhang
Population Analysis of the
LITTLE THINGS Sample
Meeting and
Events Space:
The
opening reception and workshop registration will be held on the Village Terrace
of the Meeting Village conference center. Talks and discussion will take place
in the Agave meeting room. Continental breakfast and buffet lunch will be
served in the Ocotillo room. Posters will also be displayed in the Ocotillo
and/or the Agave room. The Manzanita boardroom is available to host any
breakout sessions or working groups. Weather permitting, the banquet will be
held outdoors on the Village Terrace; otherwise, it will be held in the
Ocotillo room.
Talk Abstracts (chronological):
Dr.
Hans
Zinnecker
AIP
Potsdam and Sofia Science Center
The
upper end of the IMF: an UP2010 introductory review
In this opening talk for the
UP2010 conference, we shall discuss various models of high-mass star
formation and their predictions for the upper stellar mass limit and the
slope of the upper IMF. We also plan to theorize to what extent the upper
mass limit and the slope of the upper IMF are correlated or can vary
independently. Observational tests will be suggested to discriminate between
these possibilities.
Dr.
Cathie
Clarke
Institute of Astronomy, Cambridge
The
maximum stellar mass in clusters: evidence from observations and
hydrodynamical simulations
I shall review observational
compilations of the maximum stellar mass as a function of cluster richness
and will argue that observational data is inconclusive as to whether the data
is compatible with random sampling or with a systematic dependence of maximum
mass on cluster size. This is partly due to the fact that the data is skewed
by the way that objects are selected in observational surveys and partly
because the level of scatter expected from random sampling means that it is
hard to discern unambiguous systematic effects without an unrealistically
large sample. I will also report on recent analyses of hydrodynamical simulations which shed some light on the shaping of the
upper IMF. In these calculations (which presently omit feedback) there is
good evidence that the upper IMF is not a single power law but shows evidence
for truncation. In the simulations this bunching of stellar masses at the
upper end is a result of a similar mass acquisition history for a small group
of stars that form early in the simulation. I will conclude that the issue of
IMF truncation in observed systems is better served by a proper statistical
analysis of the upper IMF over a reasonable range of stellar mass, rather
than by maximum stellar mass data alone; given that the statistical tools for
testing for truncation are well developed, the outstanding issue becomes one
of accurate mass determinations for large samples of early type stars.
The
galaxy-wide IMF - from star clusters to galaxies
Over the past years observations
of young and populous star clusters have shown that the stellar IMF appears
to be an invariant featureless Salpeter power-law with an exponent alpha =
2.35 for stars more massive than a few Msol. A consensus has also emerged
that most, if not all, stars form in stellar groups and star clusters, and
that the mass function of young star clusters can be described as a power-law
with an exponent beta approx. 2. These two results imply that the integrated
galactic-field IMF (IGIMF) for early-type stars cannot be a Salpeter power-law,
but that they must have a steeper exponent. This has important consequences
for the distribution of stellar remnants and for the chemo-dynamical and
photometric evolution of galaxies.
Dr.
Phillip
Massey
Lowell
Observatory
What the Stellar Content of OB Associations Tell
Us (and Not) About the Slope of the IMF and Upper Mass Cutoffs
The advent of CCD spectrometers
on large aperture telescopes allow us to obtain complete censuses of massive
stars in OB associations and clusters throughout the Local Group.Such studies allow us to measure the
degree of coevality of such regions, and to compute an IMF slope, as well as
to look for evidence of a physical upper mass limit.I will review the data in hand, and
give my own views on what these data do (and don't) tell us.
Dr.
Fernando
Selman
European Southern Observatory
Around
the Tarantula and into the Arches: a Salpeter IMF in the field and in
clusters.
The stellar IMF research that our
group has conducted in the field and cluster area of the Tarantula nebula
will be presented together with our latest work in the Arches cluster near
the galactic center. We propose that the ionizing cluster of the Tarantula
has the best determined stellar IMF and should
define what we call Salpeter. We also show that there is no contradiction in
principle to have the same stellar mass function in clusters and in the field
population independently of what the cluster mass function is.
Dr.
Fernando
Comeron
European Southern Observatory
RCW
108: Massive star formation in a nearby troubled environment
At 1.3 kpc from the Sun, RCW 108
is the region hosting the latest star forming
episode of the extended Ara OB1 association. It is also one of the most
promising examples where triggered star formation may be going on at present.
The trigger is the nearby cluster NGC 6193, which is clearly eroding a
molecular cloud producing a bright, rim-shaped HII region. The most prominent
star forming site in RCW 108, IRAS 16362-4845, is a compact HII region
embedded in the molecular cloud where infrared images reveal a moderately
rich cluster. Deep, adaptive-optics-assisted imaging of this cluster shows
its weird appearance, characterized by a marked scarcity of faint members and
a lack of central concentration of its brightest stars. A detailed analysis
of the near-infrared spectral energy distribution of the cluster members
confirms that the IRAS 16362-4845 is characterized by a top-heavy stellar
mass function, with a very shallow slope that extends all the way from the
most massive, late O-type stars of the cluster down to subsolar masses. Given
the peculiar environment in which IRAS 16362-4845 resides, it is tempting to
relate the unusual features of its embedded stellar population to the
injection of energy from the most massive members of the neighboring NGC 6193
into its parental cloud. This supports the view that star formation in
heavily disturbed environments tends to give rise to unusual stellar mass
functions dominated by massive stars, and provides a nearby example where the
outcome can be observed in remarkable detail.
Dr.
Andrea
Stolte
University of Cologne
Clusters
near the center of the Galaxy - how weird is their IMF?
It has been argued on theoretical
grounds that the IMF in the hot, UV-rich Galactic center environment might be
biased to high-mass stars. Several studies made the attempt to derive the
stellar mass function in Galactic center starburst clusters, as well as in
the nuclear cluster itself. While there is indirect evidence for an
overproduction of massive stars, which may indicate a top-heavy IMF, the
direct observations of the MF are subject to large uncertainties, such as
field contamination, age and distance estimation, cluster membership, etc.
Especially the problem of field contamination and membership determination
has become more accessible with high-angular resolution proper motion studies
of Galactic center starburst clusters. Given the large stellar densities
observed along the line of sight towards the GC, proper motion membership
studies allow realistic estimates of the present-day MF for the first time.
Yet, dynamical evolution also alters the appearance of the IMF and has to be
considered when progressing from the present-day MF to the IMF. First results
from the starburst cluster proper motion campaign will be presented to
display the effects of field star contamination in the dense GC environment,
and the biasing observational effects on the IMF and possible solutions will
be presented to raise discussion among the audience.
Ms.
Katharine
Johnston
CfA /
Universty of St. Andrews
Probing
the origin of the IMF in regions of massive star formation
In this talk I will present
results from our survey of ionized gas at 3.6 cm towards 31 intermediate- and
high mass clumps detected in previous millimeter continuum observations
(Johnston et al. 2009). With these observations, we have studied the
relationship between the star forming gas, traced by millimeter continuum
emission from dust, and the ionized gas created by massive stars. Our results
suggest there is a relationship between the observed clump mass and the mass
of the ionizing massive stars within it, which is consistent with a power
law. This result is comparable with a similar relationship found between the
maximum stellar mass in young clusters and the total cluster mass (e.g.
Larson 2003 and Weidner et al. 2009), suggesting that this relationship is
set early-on in the history of the cluster by the
amount of available star forming gas. I will also present preliminary results
using a larger sample of compact HII regions embedded in molecular clouds, to
investigate whether at high masses this relationship diverges from the simple
power law expected when stars are drawn from a canonical IMF - an effect that
may be due to stellar feedback.
Dr.
Jessica
Lu
Caltech
Mass
Functions for Young Starburst Clusters in Different Milky Way Environments
We present results from
observations of several massive (>10^4 Msun), young star clusters both in
the disk and nucleus of our Galaxy. Using Keck laser guide star adaptive
optics, we obtain high-precisionproper motions to identify individual cluster members
and construct mass functions from multi-color, near-infrared photometry. The
mass functions for these clusters are compared to search for environmental
dependences.
Prof.
Sally
Oey
University of Michigan
OB
Stars in Stochastic Regimes
The highest-mass stars have the
lowest frequency in the stellar IMF, and they are also the most easily
observed stars. Thus, the counting statistics for OB stars provide
important tests for the fundamental nature and quantitative parameters of the
IMF. We first examine some local statistics for the stellar upper-mass
limit itself. Then, we examine the parameter space and statistics for
extremely sparse clusters in the SMC that contain OB stars. We find that
thus far, these locally observed counting statistics are consistent with a
constant stellar upper-mass limit. We also discuss whether clusters are
distributed fundamentally by mass, or by cluster membership number.
Dr.
Jorick
Vink
Armagh
Observatory
How
massive is the most massive star?
The current masses found for the
most massive stars in clusters depend heavily on the mass-loss history since
birth. I will present the latest mass-loss predictions for the most massive
stars in our Universe (in the mass range 60-300 solar masses) using a novel
hydrodynamic method that includes the important effects of multiple photons
interactions, predicting the rate of mass loss and the wind terminal velocity
simultaneously. I will subsequently discuss the controversial issue of
whether one would theoretically expect there to be an upper mass limit, and
whether this should be metallicity dependent.
Dr.
Mark
Krumholz
UC Santa Cruz
How
Does Radiation Feedback Affect Fragmentation and the IMF?
I discuss the results of recent
radiation-hydrodynamic simulations of the formation of stars and star
clusters, with primary focus on how radiation feedback affects fragmentation
and the mass function of the resulting stars. I show that radiation feedback
strongly affects how gas fragments, and that this effect favors the formation
of more massive stars in regions of high surface density. I discuss the
implications of this result for studies of the IMF.
Dr.
Rowan
Smith
Institut
für Theoretische Astrophysik - Universität Heidelberg
Can
environmental conditions affect the upper end of the IMF?
The shape of the stellar initial
mass function (IMF) is an important ingredient in our attempts to model the
evolution of the Universe through cosmic time. Typically the form of the IMF
is assumed to follow a universal power-law, roughly consistent with the value
originally proposed by Salpeter. However the exact form of the IMF is still
under debate and in particular, the question still remains open as to whether
the IMF depends on the environmental conditions within particular star
forming regions. We present recent numerical work that starts to address how
the physical and environmental conditions within star-forming regions can
influence both the mass function of clusters, and the stellar mass function
inside these clusters. Rather than adopting a prescribed equation of state
for the gas, we model the main heating and cooling processes directly. In our
first set of calculations we focus on how the build-up of clusters and the
properties of the stars within them, and in particular the massive stars, are
influenced by the metallicity of the gas and the strength of the interstellar
radiation field. We shall then examine how the massive end of the IMF is
constructed from the gas in a simulated GMC by directly tracing the link
between bound cores and the stellar IMF. The collapse of cores to form
stellar systems proceeds highly anisotropically, and accretion is primarily
along dense filaments. This means that the evolution of the core mass
function to the IMF depends on environmental conditions and core geometry in
addition to the core masses. We show that for massive stars, accretion from
diffuse ``clump'' gas is the dominant contribution to the final stellar mass.
This suggests that the properties of the entire cluster-forming region are
important when setting the upper end of the IMF.
Prof.
Nick
Scoville
Caltech
Determining
the Upper End Requires Knowing the Lower End
Measuring variations at the high
mass end requires knowing the low mass end since these are always relative to
the mass of low mass stars. I discuss a new observational constraint on the
low mass end which when seen requires significant masses of stars down to ~1
Msun.
Dr.
Edvige
Corbelli
INAF-Osservatorio di Arcetri
The
Cluster Birthline and the formation of stellar clusters in M33
A new method to analyze the IMF
at the high mass end in Young Stellar Clusters is presented. Its
applicability rely on the determination of the
bolometric luminosity of the newly born clusters which is usually done
through multi-wavelength Spectral Energy Distribution analysis, using
accurate photometry and appropriate theoretical spectral models.
Prof.
Daniela
Calzetti
University of Massachusetts Dept. of
Astronomy
A New
Approach to Measuring the Stellar IMF
We present
a method for investigating variations in the upper end of the stellar Initial
Mass Function (IMF) by probing the production rate of ionizing photons in
unresolved, compact star clusters with ages < 10 Myr and with different
masses. We test this method on the young cluster population in the nearby
galaxies NGC5194 (M51a) and NGC5236 (M83), for which multi--wavelength
observations from the Hubble Space Telescope are
available. Our results indicate that the proposed method can probe the upper
end of the IMF in galaxies located out to at least ~10 Mpc, i.e., a factor
~200 further away than possible by counting individual stars in young compact
clusters. Our results for the two galaxies show no obvious dependence of the
upper mass end of the IMF on the mass of the star cluster, down to ~1000
M_sun, although more extensive analyses involving lower mass clusters and
other galaxies are needed to confirm this conclusion.
Dr.
Miguel
Cerviño
IAA-CSIC
From
CMDs to Integrated properties: Probabilistic synthesis models
In this contribution I would
present a probabilistic synthesis model approach that connect smoothly CMD
analysis with the integrated properties of stellar systems. This approach
allows to explain/evaluate size-of-sample effects in the inference of M_up in
both resolved and non-resolved stellar systems. It allows allows one to
evaluate the amount of information that would be obtained from single
observations and provides a framework to study large samples of stellar
systems. In the talk I will focus on the inference of M_up of the IMF, in
particular the size-of-sample with fixed M_up vs M_up(Mcl)
dichotomy. I also investigate the relevance of the ICMF in both the
integrated light and chemical evolution of galaxies.
Dr.
Hans
Zinnecker
AIP
Potsdam and Sofia Science Center
The
Chances of Massive Star Collisions in the Center of the R136 Cluster Core
The observed stellar number
density of massive stars in the center of the dense core of the R136 cluster
in the LMC is high enough to enable stellar collisions to occur within the
short Main-Sequence lifetime of very massive stars (100 Mo). This has
implications for the uppermost IMF and its relation to gamma ray burst
progenitors.
Dr.
Brad
Whitmore
STScI
Luminous
Stars in Galaxies Beyond 3 Mpc
I am mainly interested in the
formation and destruction of young star clusters in nearby star forming
galaxies such as the Antennae, M83, and M51. One of the first analysis steps
is to throw out all those pesky stars that keep contaminating my young cluster
samples. Recently, spurred on by our new WFC3 Early Release Science data of
galaxies including M83, NGC 4214, M82, NGC 2841, and Cen A, we began taking a
closer look at the stellar component. Questions we are addressing are: 1)
what are the most luminous stars, 2) how can we use them to help study the
destruction of star clusters and the population of the field, 3) what
fraction of stars, at least the bright stars, are formed in the field, in
associations, and in compact clusters.
Dr.
Dan
Weisz
University of Minnesota
Constraints
on the Field Star IMF from Resolved Stellar Populations based Star Formation
Histories
Using HST/ACS observations of
resolved stellar populations in nearby galaxies (e.g., ANGST, LCID), I
explore the constraints one can place on the field star IMF from star
formation histories (SFHs) derived from synthetic color-magnitude diagram
(CMD) fitting.In particular, I
show how reasonable variations in the slope of the IMF, relative to a
Salpeter slope, lead to only minor changes in the SFHs.This shows that CMD-SFH fitting
parameter space has a broad minimum with respect to IMF variations and implies
that CMD based SFHs can only provide weak constraints on the stellar
IMF.Further, I demonstrate how
other uncertainties, e.g., metallicities, isochrone degeneracies, in the CMD
based SFH fitting process also pose a challenge to measuring the effects of
variations in the IMF.
Dr.
Janice
Lee
Carnegie Institution for Science
UV/H-alpha
Turmoil
The UV capabilities of GALEX have
revealed that there may be more star formation in low-density environments
than previously recognized. Until GALEX, a great deal of our
understanding of star formation in the local universe had been based on
H-alpha observations, but recent studies have shown that the H-alpha
luminosity appears to underestimate the star formation rate in dwarf and low
surface brightness galaxies, as well as in the extended disks of spirals. I
will present a study using a complete sample of ~300 spiral and irregular
galaxies in the 11 Mpc Local Volume, that establishes this systematic
trend with a significant sample of dwarf galaxies with SFRs from 0.1 Msun/yr
down to 0.0001 Msun/yr. Such trends have been cited by some
as evidence that the stellar initial mass function is deficient in high-mass
stars in low-density environments. I discuss this and a range of other
explanations.
Prof.
Gerhardt
Meurer
University of Western Australia/JHU
Upper-End
IMF Variations Deduced From HI Selected Galaxies
Since H-alpha traces the presence
of ionizing UV emission, which requires O stars (M* > 20 Msun), and vacuum
UV emission traces the presence of both O and B stars (M* > 3 Msun), the
flux ratio H-alpha/FUV strongly depends on the IMF.I will show how our H-alpha/FUV results from the SINGG and
SUNGG surveys indicates that the IMF is variable,
depending primarily on stellar mass density.Alternative interpretations of our results will be
critically examined.I will also
show recent work by our team on local H-alpha/FUV variations within
galaxies.
Dr.
Alessandro
Boselli
Laboratoire d'Astrophysique de
Marseille France
High
Mass Star Formation in Normal Late-Type Galaxies: Observational Constraints
to the IMF
We use H-alpha and
far-ultraviolet (FUV, 1539 Ang) GALEX data for a large sample of nearby
objects to study the high mass (m > 2 Msun) star formation activity of
normal late-type galaxies. The data are corrected for dust attenuation using
the most accurate techniques at present available, namely the Balmer
decrement for H-alpha data and the total far-infrared
to FUV flux ratio for GALEX data. The sample shows a highly dispersed
distribution in the H-alpha to FUV flux ratio (Log f (H-alpha)/f (FUV)) =
1.10 ± 0.34 indicating that two of the most commonly used star formation
tracers give star formation rates with uncertainties up to a factor of 2-3.
The high dispersion is partly due to the presence of AGN, where the UV and
the H-alpha emission can be contaminated by nuclear activity, highly inclined
galaxies, for which the applied extinction corrections are probably
inaccurate, or starburst galaxies, where the stationarity in the star
formation history required for transforming H-alpha and UV luminosities into
star formation rates is not satisfied. Excluding these objects, normal
late-type galaxies have Log f (H-alpha)/f (FUV) = 0.94 ± 0.16, which
corresponds to an uncertainty of~50% on the SFR. The H-alpha to FUV flux ratio of the observed
galaxies increases with their total stellar mass. If limited to normal star
forming galaxies, however, this relationship reduces to a weak trend that
might be totally removed using different extinction correction recipes. In
these objects the H-alpha to FUV flux ratio seems also barely related with
the FUV-H colour, the H band effective surface brightness, the total star
formation activity and the gas fraction. The data are consistent with a
Kroupa (2001) and Salpeter initial mass function in the high mass stellar
range (m > 2 Msun) and imply, for a Salpeter IMF, that the variations of
the slope alpha cannot exceed 0.25, from alpha = 2.35 for massive galaxies to
alpha = 2.60 in low luminosity systems. We show however that these observed
trends, if real, can be due to the different micro history of star formation
in massive galaxies with respect to dwarf systems.
Dr.
David
Thilker
The Johns Hopkins University
The
role of extended ultraviolet disk (XUV-disk) galaxies in the IMF controversy
The recognition of spatially
extended ultraviolet disks (XUV disks) in nearly 30\% of nearby spiral
galaxies partially motivated recent considerations of a variable upper
IMF.Particularly intriguing are
the XUV-disks which do not exhibit a comparably
extended distribution of HII regions.We review our observational understanding of the XUV-disk phenomenon,
based on a comprehensive GALEX survey of 3000+ local galaxies
which examines early-type galaxies as well as spirals. One aim was to
compile a statistically-significant reference sample of XUV-disk UV-emitting
complexes for which the distribution function of L(H-alpha)/L(UV)
could be measured and then compared with predictions from cluster population
models incorporating stochasticity and genuine IMF variability. If time
allows, we will also discuss HST UV-optical analysis of selected XUV-disks.
Dr.
John
Eldridge
Institute of Astronomy University of
Cambridge
How
star-formation rate indicators vary with the IMF and how it is sampled.
To gain understanding from
observations of stellar populations in galaxies theoretical models are
required. Using our state-of-the-art and highly adaptable binary population
and spectral synthesis code (BPASS) we are able to produced detailed models
for comparison to observations. Importantly these models for the first time
included detailed binary models so that the varied effects of binary
evolution are implicitly included in our model stellar populations and
spectra. We will present our latest results on how varying the IMF, and more
importantly how it is sampled, effect observable
details of stellar populations in star-forming galaxies. We take the example
of the ratio of the star-formation rates estimated from the H(alpha) line and from the FUV flux. We find that the
trend in the mean value and scatter around the mean can provide some
indication on how the IMF is sampled. Currently the best match is found when
the IMF is sampled randomly rather than there maximum mass of a star in a
cluster being dependent on the mass of the cluster however further study is
required to prove this conclusively. We will also briefly summarize other
comparisons between BPASS models and observations that provide similar
constraints and insight.
Dr.
Benjamin
Johnson
Institute of Astronomy
Fitting
the UV through IR SED of Galaxies in the Local Volume
The distribution of the Halpha/UV
ratio in local, low-luminosity galaxies is suggestive of a varying high-mass
IMF, though several additional effects may be responsible.I will describe the types of star
formation history (SFH) and dust attenuation distributions that are required
to explain these ratios -- as well as the UV through IR spectral energy
distribution -- under the assumption that the IMF does not vary.This is accomplished through the
quantitative comparison of the observed integrated SED and Halpha/UV ratios
of nearby galaxies to large suites of stellar population synthesis (SPS)
models.These SPS models include
bursts of star formation and far-infrared emission from dust. The sample of
galaxies that I will consider is drawn from the Local Volume Legacy Survey which obtained UV (GALEX), H-alpha, and IR
(Spitzer) observations of a magnitude limited sample of galaxies within
11Mpc.In addition to describing
the physical properties (including stellar mass, metallicity, and dust
attenuation) of the Local Volume galaxies thus obtained, I will consider
additional independent lines of evidence to assess whether the SFHs required
by SPS modeling with a universal IMF are a viable possibility for
low-luminosity, nearby galaxies.
Dr.
Erik
Hoversten
Penn State
Evidence
for IMF Variations from the Intergrated Light of SDSS Galaxies
We present an extension of the
Hoversten & Glazebrook (2008) study of the IMF in a sample of 130,000
actively star forming galaxies in the Sloan Digital Sky Survey (SDSS). H
alpha equivalent widths (EW) are compared to broadband colors, following Kennicutt
(1983), and H delta absorption measurements to constrain the IMF within the
3" SDSS apertures which contain on average 25%
of the total light from the galaxies. In this parameter space the effects of
the age of the stellar population are largely orthogonal to those of the IMF
and the effects of metallicity are small compared to IMF variations.We find that for luminous galaxies
the agreement with a universal IMF is good. However, low luminosity galaxies
appear to exhibit IMF variations above what can be attributed to
systematics.We show similar
variations as a function of r-band surface brightness, where low surface
brightness galaxies are deficient in massive stars.Finally, we show that at fixed luminosities IMF variations
as a function of surface brightness persist, as well as vice versa.
Mr.
Joerg
Dabringhausen
University of Bonn
Top-heavy
IMFs in ultra-compact dwarf galaxies?
Ultra compact dwarf galaxies
(UCDs) are dense stellar systems at the border between massive star-clusters
and small galaxies. The perhaps most remarkable finding about them is that
their average optical mass-to-light (M/L) ratio cannot be explained by
stellar populations with the canonical stellar initial mass function (IMF).
It seems likely from this perspective that UCDs have non-canonical IMFs,
since it is doubtful that non-baryonic dark matter can accumulate enough on
the scales of UCDs for influencing their dynamics significantly. In aged
stellar systems like the UCDs, a top-heavy IMF could however provide unseen
mass by an abundance of stellar remnants. Such a variation of the IMF can be
understood if UCDs represent a case of rapid star-formation in an extremely
dense environment. While top-heavy IMFs imply a much heavier mass-loss
shortly after the formation of a stellar system, this process does not
necessarily dissolve the UCDs. Their formation with a top-heavy IMF would
therefore not contradict their existence.
Dr.
Jan
Pflamm-Altenburg
AIfA Bonn
Applications
of the IGIMF-theory
The functional form of the
galaxy-wide stellar initial mass function is of fundamental importance for
the transformation of observational quantities into physical quantities of
galaxies. So far this galaxy-wide stellar initial mass function has been
assumed to be identical to the stellar initial mass function (IMF) observed
directly in star clusters. But the nature of clustered star formation, i.e.
stars form predominantly in compact star clusters rather than uniformly
distributed over the whole galaxy, requires the galaxy-wide IMF to be
calculated by adding all IMFs of all young star clusters. This integrated
galactic stellar initial mass function (IGIMF) is steeper than the canonical
IMF in star clusters and steepens with decreasing SFR, leading to fundamental
new insights and understanding of star forming properties of galaxies. In
this talk I will summarize all applications of the IGIMF-theory made so far,
and present new possibilities to test its validity.
Dr.
Bruno
Jungwiert
Astronomical
Institute ASCR - Prague
N-body
simulations of disk galaxies with long-term stellar mass-loss within the
IGIMF framework
We present N-body/gas-dynamical
simulations of disk galaxies aimed at quantifying the IGIMF effect combined
with the long-term stellar mass-loss from low-mass and intermediate-mass
stars on galaxy dynamics, star formation rate, stellar build-up and gas
depletion time-scales as well as on abundance gradients.
Dr.
Francesco
Calura
INAF- Oss. di
Trieste/Univ. Central Lancashire
The
Role of the IGIMF in the chemical evolution of the solar neighbourhood
We test the effects of the
integrated galactic initial mass function (IGIMF) on the chemical evolution
of the solar neighbourhood.The
IGIMF (Weidner & Kroupa 2005) is computed from the convolution of the
stellar initial mass function (IMF), i.e. the mass function of single stars,
and the embedded cluster mass function, i.e. a power law with index
beta.By taking into
account also the fact that the maximum achievable stellar mass is a function
of the total mass of the cluster, the result of the convolution is a
time-varying IMF which depends on the star formation
rate.We applied this
formalism to a chemical evolution model for the solar neighbourhood and
compared the results obtained by assuming three possible values for beta with
the results obtained by means of a standard, well-tested,
constant IMF. In general, a lower absolute value of beta implies a flatter
IGIMF, hence a larger number of massive stars and larger metal ejection
rates.This translates into
higher Type Ia and II supernova rates, higher mass ejection rates from
massive stars and a larger amount of gas available for star formation,
coupled with lower present-day stellar mass densities.Lower values of beta correspond
also to higher metallicities and higher[alpha/Fe] values at a given metallicity. We consider a large set of
chemical evolution observables and test which value of beta provides the best
match to all of these constraints.We also discuss the importance of the present day stellar mass
function(PDMF) in providing a
way to disentangle among various assumptions for beta.Our results indicate that the
IGIMF computed with beta=2 should be considered the best since it allows us
to reproduce the observed PDMF and to account for most of the chemical
evolution constraints considered in this work.
Prof.
Pavel
Kroupa
Argelander Institute for Astronomy
Bonn
Some
implications of the variable galaxy-wide IMF
The integrated galactic initial
mass function (IGIMF) results from adding the IMFs in all forming star
clusters in a galaxy. The IGIMF turns out to be deficient in massive stars,
and the deficiency increases for galaxies with lower star-formation rates.
Since massive stars are usually the tracers of current star-formation
activity in a galaxy, the star-formation rates need to be revised. I will
discuss the star-formation behaviour of galaxies within the IGIMF framework which may have some interesting implications for
fundamental physics.
Dr.
Barry
Madore
Carnegie Observatories
What Is
This Thing Called the Schmidt Law?
In an extragalactic context the
Schmidt Law began as a very simple power-law description of how current
high-mass star formation scales with coincident and contemporary neutral
hydrogen surface density. On the other hand theorists often use the Schmidt
Law formalism as a simplified means of modeling the sensitivity of future
star formation to present total gas volume density. Subsequent
generalizations from a local Schmidt Law to a global one has added a
layer of complexity that has not been fully appreciated or completely
explored. We will attempt to make explicit and then reconcile these various
views of what the Schmidt Law is. And then we will explore how the Schmidt
Law can best be calibrated and used, by presenting a combination of simple
mathematical models, computer simulations and new data from space (GALEX) and
the ground (THINGS). The tracers of high-mass star
formation and their various timescales figure prominently in this analysis.
Miss
Madusha
Gunawardhana
Macquarie University Sydney
The
dependence of the stellar initial mass function on the galaxy star formation
rate
Recent studies based on
non-traditional approaches (e.g., integrated properties of large samples of
galaxies, carbon-enhanced metal-poor stars) have suggested a non-universal
IMF that varies between galaxies and possibly evolves with time. The study of
the implications of an evolving or spatially variable IMF, and possible
observational approaches to constraining this quantity, is fundamental to a
broad range of galaxy evolution research. I will present the results of a
study conducted using GAMA (Galaxy And Mass Assembly) spectroscopic data that
show a strong underlying IMF dependency on the SFR of the host galaxy,
indicating that high star formation rate systems are characterized by a
shallow IMF slope. This result is shown to be robust against a variety of
potential instrumental and sampling biases. It is supported by, and provides
an explanation for, the results of numerous recent explorations implying a
variation or evolution in the IMF.
Dr.
Claus
Leitherer
STScI
Constraints
on the Upper IMF from Ultraviolet Spectral Lines
Stellar-wind lines in the
ultraviolet are an indicator of recent massive star formation and are
sensitive to the IMF of the most massive stars. I will discuss the behavior
of some of the key lines and how they are affected by the degeneracy between
IMF, age, and metallicity. I will give examples of observations of nearby and
distant galaxies and evaluate whether there is evidence for a variable IMF.
Dr.
James
Neill
Caltech
Measuring
the Upper End of the IMF with Supernovae
Supernovae arise from progenitor
stars occupying the upper end of the initial mass function.Their extreme brightness allows
individual massive stars to be detected at cosmic distances, lending
supernovae great potential as tracers of the upper end of the IMF and it's
evolution. Exploiting this potential requires progress in many areas of
supernova science.These include
understanding the progenitor masses that produce various types of supernovae
and accurately characterizing the supernova outburst and the environment in
which it was produced.I will
present some recent work identifying the environmental conditions that
produce the most luminous supernovae, believed to arise from stars with
masses greater than 100 solar masses.I will use the presence of these extreme supernovae in small
star-forming dwarfs to test our understanding of the upper end of the IMF.
Dr.
Jeff
Cooke
Caltech
Type
IIn supernova detections in z ~ 2 Lyman break galaxies: Probing the IMF
directly
Type IIn supernovae (SNe IIn)
exhibit extremely luminous ultraviolet continua during outburst and extremely
luminous, long-lived narrow ultraviolet and optical emission lines.These properties have enabled
successful high redshift detections in archival imaging and late-time
spectroscopic confirmation and study.I will present our method of detecting z > 2 SNe IIn and the first
6+ spectroscopic confirmations at 2 < z < 3 using the
Canada-France-Hawaii Telescope Legacy Survey and the Keck Telescopes.Because SNe IIn are believed to have
massive progenitors, the well-defined volume and well-understood host galaxy
population surveyed using this method facilitate a direct test of the
high-mass end of the high-redshift IMF from a relatively small number of
detections.I will discuss the
implications of the current detections on the form of the IMF and the
enhancement of these results from 2 < z < 6 via upcoming large, deep
synoptic surveys such as Hyper SuprimeCam, the LSST, and future 30m-class
telescopes.
Mr.
Loïc
Le Tiran
GEPI Observatoire
de Paris
The
turbulent ISM of galaxies about 10 Gyrs ago: an impact on their IMF?
I will present observations of 10
massive galaxies as seen as they were 9 Gyrs ago with the integral-field
spectroscopy using SINFONI from the ESO-VLT, combined with data obtained from
the DEEP2 Survey. I will first paint a brief picture of the physical
conditions at work in these galaxies: they exhibit complex morphologies, high
star formation and are so pressure dominated they are likely to drive winds.
Moreover, their ratio of Hα to FUV flux to R-band luminosity surface
brightnesses indicates that perhaps their initial mass function is flatter
than Salpeter at the high mass end, as has been suggested recently for some
local galaxies. It may be that high turbulence is responsible for skewing the
IMF towards more mass stars as has been suggested by some theories of
star-formation.
Mr.
Chris
Hayward
Harvard-Smithsonian Center for
Astrophysics
The IMF
in z~2 Starbursts: Evidence for Minimal Variations from LocalMass Functions
Matching the observed abundance
and redshift distribution of submillimeter galaxies (SMGs), some of the most
luminous, rapidly star-forming galaxies in the Universe, has been a notorious
problem for galaxy formation models. Typically, solutions to this
problem have required ad hoc IMF variations at high redshift, ranging from a
"bottom-light" IMF (Dave et al. 2009) to the extreme
"flat" IMF (Baugh et al. 2005). I will argue that significant IMF
modifications are not justified by the apparent conflict between observed SMG
number counts and those predicted by previous models. I will present a
multi-scale model for the formation of SMGs which
can accurately reproduce the observed UV-mm wave SED, inferred physical
properties, and observed number counts of this population. Our model,
the first to combine high-resolution N-body/hydrodynamic simulations and dust
radiative transfer in a cosmological framework, is able to match observed 850
micron number counts even while utilizing a "standard" Kroupa IMF.
Mr.
Stephen
Wilkins
University
of Oxford
The
Effect of an Evolving IMF on the Cosmic Star Formation History
It has been noted by several
studies that the integral of the cosmic star formation history (CSFH)
suggests a local stellar mass density discrepant with in-situ observations.
One potential solution for this is the IMF: either through an alternative
universal IMF of some form of IMF evolution. The latter of these is
particularly interesting due to tentative recent evidence of IMF variation
and the implications for galaxy formation and evolution. In this talk the
effect of the IMF on the CSFH, the build up of stellar mass density and the
cosmic spectral energy distribution will be discussed.
Dr.
Naveen
Reddy
NOAO
Reconciling
the Star Formation and Stellar Mass Density Histories
I will review some recent work on
quantifying the systematics inherent in star formation and stellar mass
density estimates at high redshift, including luminosity-dependent dust
corrections and an accounting of the stellar mass density in UV faint
galaxies.Correcting for these
systematics results in a star formation history that agrees well with our
inferences of the stellar mass density at z~2.I will briefly discuss the implications of this result for
the evolution of the IMF and present constraints on the high mass end of the
IMF from the UV spectra of z~2-3 galaxies.
Prof.
Romeel
Davé
University of Arizona
The Odd
Meanderings of the IMF Across Cosmic Time
Our understanding of how galaxies
form is far from complete, so it seems remarkable to suggest that one can
constrain the IMF across cosmic time based on galaxy formation theory.Yet I will argue that this is now not
only possible, but makes specific predictions for mild and non-monotonic
variations in the typical IMF (more precisely, the IGIMF) of star-forming
galaxies from z~0-6.The key
observable used for such constraints is the specific star formation rate of
galaxies as a function of redshift.Current models generically predict a different evolution that
observed.One
possible reconciliation is that the IMF in typical star-forming
galaxies varies with cosmic epoch.Such IMF evolution can actually reconcile a wide range of disparate
observations, including the late evolution of cluster ellipticals, the cosmic
extragalactic background light, the number of carbon-enhanced metal poor
stars in the Galaxy, and others.While there is no smoking gun evidence for IMF variations and each data set individually can be plausibly explained by
systematic effects, the fact that a single evolving IMF broadly
explains them all makes such a scenario worth consideration.
Dr.
Eric
Murphy
Caltech/SSC
The
Possibility of Identifying Variations to the IMF at High-z Through Deep Radio
Surveys
While star-forming galaxies are
currently thought to be responsible for completely reionizing the
intergalactic medium (IGM) by z~6 (e.g., Becker et al. 2001; Fan et al.
2006), the ionizing flux arising from star formation in Lyman break galaxies
at similar redshifts (Bouwens et al. 2007, 2008) appears to fall a factor of
>~6 below the minimum value required to maintain an ionized IGM for a
given clumping factor and escape fraction under the assumption of a Salpeter
stellar initial mass function (IMF). Chary (2008) has shown that this
discrepancy can be reconciled by flattening the stellar IMF to have a slope
of ~ -1.7 if reionization occurred at z = 9 thus increasing the ionizing
photon rate. While the idea of a top heavy IMF at these epochs does not seem
completely inappropriate given that low metallicity environments will favor
the production of more high-mass stars, trying to identify such a variation
remains difficult. At such high redshifts, I will argue that deep radio
continuum observations at frequencies >10 GHz using next generation
facilities like the SKA will likely provide the most accurate measurements
for the ionizing photon rates (star formation rates) of normal galaxies sin
the non-thermal emission from such galaxies should be completely suppressed
due to the increased inverse Compton (IC) scattering off of the cosmic
microwave background (CMB), leaving only the thermal (free-free) emission
detectable.Thus, a
careful analysis of such observations in combination with future JWST
measurements of the rest-frame UV emission from the same population of
galaxies may yield the best means to search for variability in the stellar
IMF at such epochs.
Poster Abstracts (alphabetical):
Dr.
Jennifer
Donovan Meyer
Physics
and Astronomy Dept. SUNY Stony Brook Poster
Star
Formation in the Outskirts of Early Type Galaxies
GALEX has enabled the discovery
that extended star formation is not uncommon in the outskirts of spiral
galaxies. It has also enabled the discovery of low levels of star formation
in the outskirts of some early type galaxies, often coincident with the
detection of HI (when such observations are available). These regions often
lack corresponding detections in H-alpha emission, raising questions about
the IMF at work at large galactic radii. I will present a study of the
stellar populations in the outskirts of a sample of early types in the
context of the IMF discussion.
Mr.
Michele
Fumagalli
UC
Santa CruzPoster
SLUG: A
new way to Stochastically Light Up Galaxies
Stochastic star formation may
offer an alternative explanation for evidence of a varying initial mass
function (IMF). Incomplete sampling of the IMF in regions with low rates of
star formation tends to produce populations that are deficient in high mass
stars even if the underlying stellar IMF is independent of the star formation
rate. This stochastic effect, combined with stellar evolution and cluster
disruption, may explain the high UV to Ha ratio observed in dwarf galaxies
and in the outskirts of some spirals without resorting to changes in the IMF.
We present SLUG, a new code to Stochastically Light Up Galaxies as a test for
the evidence of IMF variations. SLUG populates star clusters by drawing stars
from canonical IMFs. It then follows the time evolution of the clusters using
standard stellar evolution tracks and an observationally-motivated
model for cluster disruption. For a choice of star formation rate and IMF,
SLUG outputs predictions of the distribution of cluster UV, Ha, and
bolometric luminosities with a proper treatment of stochastic star formation.
Future versions will support a range of metallicities and non-constant star
formation histories as well. Using SLUG, we are able to generate a realistic
distribution of star clusters, demonstrating the range of properties that
result from finite sampling and a random distribution of ages. This synthetic
data set provides a crucial control against which claims to detect IMF
variation must be tested. This code will be made publicly available. (SLUG is
developed by Robert da Silva, Michele Fumagalli, Mark Krumholz and Frank
Bigiel)
Prof.
Mauro
Giavalisco
University
of MassachusettsPoster
Star
Formation in Massive Galaxies at Redshift 2<4
We present evidence of different
modes of star formation in massive (10^10-10^11 M_sun) galaxies at redshift
2<4. While current samples still suffer from limited sensitivity in
comparison to the local universe, we show that the latest instrumentation has
significantly increased the range of spectral types accessible to
observations at these early epochs. We review the properties of galaxies of
various spectral types and discuss the implications for galaxy evolution in
general, focusing in particular on the possible mechanisms more likely to
drive the evolution.
Ms.
Wen-hsin
Hsu
Univerisity
of MichiganPoster
Competitive
Accretion in Sheet Geometry and the Stellar IMF
We report a set of numerical
experiments aimed at addressing the applicability of competitive accretion to
explain the high-mass end of the stellar initial mass function in initially
non-clustered environments, in contrast to most previous simulations which
have assumed formation in a cluster gravitational potential. We adopted a
simple cloud model with a sheet or flat geometry, motivated by models of
molecular cloud formation due to large-scale flows in the interstellar
medium. The experiments consisted of SPH simulations of gas accretion onto
sink particles formed rapidly from Jeans-unstable dense clumps placed
randomly in the finite as sheet. These simplifications allow us to study
accretion with a minimum of free parameters, and to develop better statistics
on the resulting mass spectra. We considered both clumps of equal mass and
Gaussian distributions of masses, and either uniform or spatially-varying
gas densities. In all cases, the sink mass function develops a power law tail
at high masses, with dN/dlogM approx M^{-Gamma}. The accretion rates of individual
sinks follow Mdot approx M^2 at high masses; this
results in a continual flattening of the slope of the mass function towards
an asymptotic form Gamma ~1 (where the Salpeter slope is Gamma = 1.35). The
asymptotic limit is most rapidly reached when starting from a relatively
broad distribution of initial sink masses. In general the resulting upper
mass slope is correlated with the maximum sink mass; higher sink masses are
found in simulations with flatter upper mass slopes. Although these
simulations are of a highly idealized situation, the results suggest that
competitive accretion may be relevant in a wider variety of environments than
previously considered, and in particular that the upper mass distribution may
generally evolve towards a limiting value of Gamma ~1.
Ms.
Hwihyun
Kim
Arizona
State UniversityPoster
Study
of Resolved Stellar Populations in M83 using HST/WFC3 Early Release Science
Data
We present a multi-wavelength
photometric study of individual stars in M83 based on observations taken as
part of the WFC3 Early Release Science (ERS) program. The central region of
M83 has been imaged in seven broad-band filters to
obtain multi-wavelength coverage from the ultra-violet to near-infrared. We
use four filters--F336W, F438W, F555W, and F814W--to measure the effective
temperature and intrinsic luminosity for ~10,000 stars. These measurements are
used to determine the recent (< 1 Gyr) star formation history of M83. We
selected 30 regions in the spiral arm and the inter-arm area of M83 and
categorize them based on their Hα morphology. To determine ages of stars
in each region, we use color-magnitude diagrams (CMD) and color-color
diagrams with the Padova Isochrones for a metallicity of Z=0.03 (1.5 Z_sun),
and compare to ages determined by cluster age-estimates from Hα
morphology and from SED fitting. The CMD and color-color diagrams of resolved
stars from the multi-band HST/WFC3 observations of M83 indicate the presence
of multiple stellar populations: the recently formed main-sequence,
He-burning blue-loop, red giant branch, and asymptotic giant branch stars.
Multi-populations of stars in the CMDs of the 30 selected regions indicate
that stars in a single region may not have formed from the same star
formation event. Also, we find that the regions with ages determined younger
than 10 Myr are located preferentially along the active star-forming region
on the spiral arm.
Dr.
Andrea
Urban
JPL/CaltechPoster
Studying
the effect of radiation and dust-gas energetics on clustered star formation
Using simulations of a
cluster-scale environment we investigate the effect of heating and cooling on
the formation of a young cluster and its mass function. Our dust-gas
energetics algorithm includes a simplified radiative transfer method,
dust-gas collisional heating, molecular cooling, and cosmic-ray ionization.
In our simulation, we find that the newly-formed
stars, by heating the dust and gas in the cluster, influence the formation of
future stars. The luminosity from the massive stars affects the mass function,
dust/gas temperature, star formation efficiency, and maximum stellar mass in
the cluster.
Dr.
Linda
Watson
Ohio
State UniversityPoster
Testing
the Star Formation Law in Bulgeless Disk Galaxies
We study the relation between gas
and star formation surface density in twenty bulgeless disk galaxies using
data from the VLA, IRAM 30m, MDM, Spitzer IRAC, and HST. Recent work has
provided constraints on the physics that sets the star formation efficiency
(SFE) in varying environments of the interstellar medium; however, a single
theory for star formation has yet to stand out among its peers. The general
motivation for our work is to test the predictive power of current theories
with substantially improved observations of late-type and low-mass
disks, which are underrepresented in most surveys. We specifically study star
formation and the properties of the cold ISM above and below the circular
velocity threshold of 120 km/s (stellar mass ~ 10^10 M_sun), where Dalcanton
et al. (2004) found that edge-on disk galaxies show an abrupt transition in
their dust scale heights. This transition also corresponds to a disk
stability transition according to the Toomre Q parameter. We will present our
study of a sample of nearby, moderately inclined galaxies that bracket this
transition velocity, focusing on their location relative to the star formation
law, an analysis of the effect of disk stability on SFE, and implications for
a general theory of star formation.
Dr.
Aida
Wofford
Space
Telescope Science InstitutePoster
The
Massive Star Initial Mass Function of Circumnuclear Clusters in M83
The circumnuclear starburst of
M83 (NGC 5236), the nearest such example, is an ideal site for studying the
massive star initial mass function (IMF) at high metallicity. We analyze
archival Hubble Space Telescope (HST) observations, including ultraviolet
imaging and spectroscopy, of compact star clusters located within M83's
starburst. We compare the observed spectra with two sets of Starburst99
models, older, semi-empirical models (Robert et al. 1993) and new fully
theoretical models based on a new synthetic library of high-resolution UV
spectra for hot massive stars (Leitherer et al. 2010). We generate single
stellar population models with metallicities of Z=0.020 and Z=0.040, using
different high mass limits and slopes for the upper IMF, and determine the
intrinsic reddenings, masses, and ages of the brightest clusters in M83's
starburst, based on the model that best fits the data.
Dr.
Ted
Wyder
CaltechPoster
H-alpha
and UV imaging of XUV disks and LSB galaxies
GALEX
observations have revealed UV emission extending far beyond the optical and
H-alpha discs of several nearby spiral galaxies, raising the question of
possible massive star deficiency, i.e. deviations from the standard
'universal' IMF at the upper end, in certain low density environments. We have
undertaken an H-alpha survey of low surface brightness galaxies observed by
GALEX and with existing HI maps with the aim of investigating the variation
of the H-alpha/UV ratio with the local density. Here we present preliminary
results for 14 such galaxies observed with the Large Format Camera on the
Palomar 200in telescope using custom narrow band filters.
Mr.
Harus
Zahid
Institute
for Astronomy UH ManoaPoster
The MZ
and LZ relation from DEEP2 at z ~ 0.8
We present results from a study
investigating the evolution of the mass-metallicity and
luminosity-metallicity relation over cosmological timescales. We determine
the metallicities from strong-line diagnostics for 940 emission line galaxies
from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) redshift survey in
the redshift range of 0.75<0.82. We determine masses by fitting the SED
inferred from photometry with stellar population synthesis models. We compare
our determination of the MZ and LZ relation with the local relation from
SDSS. We show that at z~0.8 galaxies with masses M~10^10.5 M_solar have
already achieved the level of enrichment observed in the local universe. The
mass-metallicity relation for z ~ 0.8 has slightly steeper slope than the
local relation and the mean difference in metallicity is ~0.05 dex. We
examine the luminosity-metallicity relation and determine that the slope of
the relation at z~0.8 is consistent with the local relation. The metallicity
at a given luminosity in the z~0.8 is offset from the local relation by ~0.12
dex. We attribute the discrepancy between the metallicity evolution inferred
from the mass-metallicity and luminosity-metallicity relation to luminosity
evolution in the population of blue star-forming galaxies. We infer a B-band
luminosity evolution of ~0.8 mags for the population of star-forming
galaxies. We estimate gas masses from the Schmidt-Kennicutt star formation
law and determine the effective yields for our sample. We observe an
effective yield that decreases with increasing stellar mass and take this as
evidence for the inconsequential role of galactic flows in shaping the mass-metallicity
relation. We propose that the evolution of the mass-metallicity relation is a
consequence of relative increase in the mass of metals with respect to the
mass of gas, though both are observed to decrease. One possible explanation
for such an evolution is a varying IMF.
Dr.
Hongxin
Zhang
Lowell
ObservatoryPoster
Population
Analysis of the LITTLE THINGS Sample
We have assembled a
multi-wavelength dataset, including deep interferometric HI maps, on a sample
of 41 relatively normal, nearby gas-rich dwarf (dIm) galaxies (LITTLE
THINGS). These data trace stellar populations, gas content, and dynamics for
the purpose of testing and modifying star formation models. Here we present
the results of stellar population analysis for the whole sample using
multi-wavelength broadband data from GALEX FUV to IRAC 3.6um. Considering the
extreme properties (e.g. low metallicity, low gas surface density) of these
dwarf galaxies, we experiment with various possible characteristics, such as
a steep IMF, a steep extinction law, and extreme star formation histories on
this sample. Based on our population modeling, we try to discuss the global
star formation histories for the dwarf irregular galaxies in general.
Participants:
NAME
AFFILIATION
EMAIL
Dr.
Médéric Boquien
University
of Massachusetts
boquien(at)astro.umass.edu
Dr.
Alessandro Boselli
Laboratoire
d'Astrophysique de Marseille France
Alessandro.Boselli(at)oamp.fr
Dr.
Francesco Calura
INAF-
Oss. di Trieste/Univ. Central Lancashire
fcalura(at)oats.inaf.it
Prof.
Daniela Calzetti
SOC member
University
of Massachusetts
calzetti(at)astro.umass.edu
Dr.
Miguel Cerviño
IAA-CSIC
mcs(at)iaa.es
Dr.
Cathie Clarke
Institute
of Astronomy
cclarke(at)ast.cam.ac.uk
Dr.
Fernando Comeron
European
Southern Observatory
fcomeron(at)eso.org
Dr.
Jeff Cooke
Caltech
cooke(at)astro.caltech.edu
Dr.
Edvige Corbelli
SOC member
INAF-Osservatorio
di Arcetri
edvige(at)arcetri.astro.it
Mr.
Joerg Dabringhausen
University
of Bonn
joedab(at)astro.uni-bonn.de
Mr.
Robert da Silva
UC
Santa Cruz
rdasilva.astro(at)gmail.com
Prof. Romeel
Dave
University
of Arizona
rad(at)as.arizona.edu
Dr.
Jennifer Donovan Meyer
Physics
and Astronomy Dept. SUNY Stony Brook
jen(at)astro.columbia.edu
Dr.
John Eldridge
Institute
of Astronomy University of Cambridge
jje(at)ast.cam.ac.uk
Mr.
Kerry Erickson
Caltech/JPL
kerry.d.erickson(at)jpl.nasa.gov
Dr.
Henry Ferguson
STScI
ferguson(at)stsci.edu
Mr.
Michele Fumagalli
UC
Santa Cruz
mfumagalli(at)ucolick.org
Prof.
Jay Gallagher
University
of Wiscsonin-Madison
jsg(at)astro.wisc.edu
Prof.
Mauro Giavalisco
University
of Massachusetts
mauro(at)astro.umass.edu
Miss
Madusha Gunawardhana
Macquarie
University Sydney
madusha.gunawardhana(at)
students.mq.edu.au
Mr.
Chris Hayward
Harvard-Smithsonian
Center for Astrophysics
chayward(at)cfa.harvard.edu
Mr.
Michael J. Heaton
Astrophysics
Research Institute - Liverpool John Moores University
mh(at)astro.livjm.ac.uk
Dr.
Erik Hoversten
Penn
State
hoversten(at)astro.psu.edu
Ms.
Wen-hsin Hsu
University
of Michigan
wenhsin(at)umich.edu
Dr.
Benjamin Johnson
Institute
of Astronomy
bjohnson(at)ast.cam.ac.uk
Mr.
Cliff Johnson
University
of Washington
lcjohnso(at)astro.washington.edu
Ms.
Katharine Johnston
CfA / Universty
of St. Andrews
kjohnston(at)cfa.harvard.edu
Dr.
Bruno Jungwiert
Astronomical
Institute ASCR - Prague
bruno(at)ig.cas.cz
Ms.
Hwihyun Kim
Arizona
State University
hwihyun.kim(at)asu.edu
Dr.
Iraklis Konstantopoulos
Penn State
Universty
iraklis(at)astro.psu.edu
Prof.
Pavel Kroupa
SOC member
Argelander
Institute for Astronomy Bonn
pavel(at)astro.uni-bonn.de
Dr.
Mark Krumholz
SOC member
UC
Santa Cruz
krumholz(at)ucolick.org
Mr.
Loïc Le Tiran
GEPI Observatoire
de Paris
loic.le-tiran(at)obspm.fr
Dr.
Janice Lee
SOC/LOC
co-chair
Carnegie
Observatories
jlee(at)obs.carnegiescience.edu
Dr.
Claus Leitherer
STScI
leitherer(at)stsci.edu
Dr.
Jessica Lu
Caltech
jlu(at)astro.caltech.edu
Dr.
Barry Madore
SOC member
Carnegie
Observatories
barry(at)obs.carnegiescience.edu
Prof.
Christopher Martin
SOC member
Caltech
cmartin(at)srl.caltech.edu
Dr.
Phillip Massey
Lowell
Observatory
phil.massey(at)lowell.edu
Prof.
Gerhardt Meurer
University
of Western Australia/JHU
gerhardt.meurer(at)icrar.org
Dr.
Eric Murphy
Caltech/SSC
emurphy(at)ipac.caltech.edu
Dr.
James Neill
LOC member
Caltech
neill(at)srl.caltech.edu
Prof.
Sally Oey
University
of Michigan
msoey(at)umich.edu
Dr. Jan
Pflamm-Altenburg
AIfA
Bonn
jpflamm(at)astro.uni-bonn.de
Dr.
Naveen Reddy
SOC member
NOAO
nar(at)noao.edu
Prof.
David Schiminovich
SOC member
Columbia
University
ds(at)astro.columbia.edu
Prof.
Nick Scoville
Caltech
nzs(at)astro.caltech.edu
Dr.
Mark Seibert
SOC/LOC
co-chair
Carnegie
Observatories
mseibert(at)obs.carnegiescience.edu
Dr.
Fernando Selman
European
Southern Observatory
fselman(at)eso.org
Dr.
Rowan Smith
Institut
für Theoretische Astrophysik - Universität Heidelberg