1,276 research outputs found
Hubble Space Telescope images of submillimeter sources: large, irregular galaxies at high redshift
We present new Hubble Space Telescope STIS, high-resolution optical imaging
of a sample of 13 submillimeter (submm) luminous galaxies, for which the
optical emission has been pinpointed either through radio-1.4 GHz or millimeter
interferometry. We find a predominance of irregular and complex morphologies in
the sample, suggesting that mergers are likely common for submm galaxies. The
component separation in these objects are on average a factor two larger than
local galaxies with similarly high bolometric luminosities. The sizes and star
formation rates of the submm galaxies are consistent with the maximal star
formation rate densities of 20 Msun kpc^{-2} in local starburst galaxies
(Lehnert & Heckman 1996). We derive quantitative morphological information for
the optical galaxies hosting the submm emission; total and isophotal
magnitudes, Petrosian radius, effective radius, concentration, aspect ratio,
surface brightness, and asymmetry. We compare these morphological indices with
those of other galaxies lying within the same STIS images. Most strikingly, we
find ~70% of the submm galaxies to be extraordinarily large and elongated
relative to the field population, regardless of optical magnitude. Comparison
of the submm galaxy morphologies with those of optically selected galaxies at
z~2-3 reveal the submm galaxies to be a morphologically distinct population,
with generally larger sizes, higher concentrations and more prevalent
major-merger configurations.Comment: 16 pages, 6 figures, scheduled for ApJ, v599, Dec10, 2003. Minor
edits. For version with higher resolution figures, see
http://www.submm.caltech.edu/~schapman/ms_v3.ps.g
The Structures of Distant Galaxies V: The Evolution of Galaxy Structure in Stellar Mass at z < 1
Galaxy structure and morphology is nearly always studied using the light
originating from stars, however ideally one is interested in measuring
structure using the stellar mass distribution. Not only does stellar mass trace
out the underlying distribution of matter, it also minimises the effects of
star formation and dust on the appearance and structure of a galaxy. We present
in this paper a study of the stellar mass distributions and structures of
galaxies at z<1 as found within the GOODS fields. We use pixel by pixel
K-corrections to construct stellar mass and mass-to-light ratio maps of 560
galaxies of known morphology at magnitudes z_{850}<24. We measure structural
and size parameters using these stellar mass maps, as well as on ACS BViz band
imaging. This includes investigating the structural CAS-Gini-M_{20} parameters
and half-light radius for each galaxy. We compare structural parameters and
half-light radii in the ACS z_{850}-band and stellar mass maps, finding no
systematic bias introduced by measuring galaxy sizes in z_{850}. We furthermore
investigate relations between structural parameters in the ACS BViz bands and
stellar mass maps, and compare our result to previous morphological studies.
Combinations of various parameters in stellar mass generally reveal clear
separations between early and late type morphologies, but cannot easily
distinguish between star formation and dynamically disturbed systems. We also
show that while ellipticals and early-type spirals have fairly constant CAS
values at z<1 we find a tendency for late-type spiral and peculiar
morphological types to have a higher A(M_{*}) at higher redshift. We argue that
this, and the large fraction of peculiars that appear spiral-like in stellar
mass maps, are possible evidence for either an active bulge formation in some
late-type disks at z<1 or the presence of minor merger events.Comment: 27 pages, MNRAS in pres
The Structures of Distant Galaxies I: Galaxy Structures and the Merger Rate to z~3 in the Hubble Ultra-Deep Field
This paper begins a series in which we examine the structures of distant
galaxies to directly determine the history of their formation modes. We start
this series by examining the structures of z_F850LP < 27 galaxies in the Hubble
Ultra-Deep field, the deepest high-resolution optical image taken to date. We
investigate a few basic features of galaxy structure using this image. These
include: (1) The agreement of visual eye-ball classifications and
non-parametric quantitative (CAS, Gini/M_20) methods; (2) How distant galaxy
quantitative structures can vary as a function of rest-frame wavelength; and
(3) The evolution of distant galaxy structures up to z~3. One of our major
conclusions is that the majority of galaxies with z_850 < 27 are peculiar in
appearance, and that galaxy assembly is rapidly occurring at these magnitudes,
even up to the present time. We find a general agreement between galaxy
classification by eye and through quantitative methods, as well as a general
agreement between the CAS and the Gini/M_20 parameters. We find that the
Gini/M_20 method appears to find a larger number of galaxy mergers than the CAS
system, but contains a larger contamination from non-mergers. We furthermore
calculate the merger rate of galaxies in the UDF up to z~3, finding an increase
with redshift as well as stellar mass, confirming previous work in the Hubble
Deep Field. We find that massive galaxies with M_{*} > 10^10 M_0 undergo
4.3_+0.8^-0.8 major galaxy mergers at z < 3, with all of this merging occurring
at z > 1.Comment: MNRAS, submitte
The Tumultuous Formation of the Hubble Sequence at z > 1 Examined with HST/WFC3 Observations of the Hubble Ultra Deep Field
We examine in this paper a stellar mass selected sample of galaxies at 1 < z
< 3 within the Hubble Ultra Deep Field, utilising WFC3 imaging to study the
rest-frame optical morphological distribution of galaxies at this epoch. We
measure how apparent morphologies (disk, elliptical, peculiar) correlate with
physical properties, such as quantitative structure and spectral-types. One
primary result is that apparent morphology does not correlate strongly with
stellar populations, nor with galaxy structure at this epoch, suggesting a
chaotic formation history for Hubble types at z > 1. By using a locally defined
definition of disk and elliptical galaxies based on structure and
spectral-type, we find no true ellipticals at z > 2, and a fraction of
3.2+/-2.3% at 1.5 < z < 2. Local counterparts of disk galaxies are at a similar
level of 7-10%, much lower than the 75% fraction at lower redshifts. We further
compare WFC3 images with the rest-frame UV view of galaxies from ACS imaging,
showing that galaxies imaged with ACS that appear peculiar often contain an
`elliptical' like morphology in WFC3. We show through several simulations that
this larger fraction of elliptical-like galaxies is partially due to the
courser PSF of WFC3, and that the `elliptical' class very likely includes
early-type disks. We also measure the merger history for our sample using CAS
parameters, finding a redshift evolution increasing with redshift, and a peak
merger fraction of ~30% at z~2 for the most massive galaxies with M_*> 10^{10}
M_sol, consistent with previous results from ACS and NICMOS. We compare our
results to semi-analytical model results and find a relatively good agreement
between our morphological break-down and the predictions. Finally, we argue
that the peculiars, ellipticals and peculiar ellipticals have similar
properties, suggesting similar formation modes, likely driven by major mergers.Comment: 21 pages, submitted to MNRA
The Formation of Low-Mass Cluster Galaxies and the Universal Initial Galaxy Mass Function
Clusters of galaxies have an observed over-density of low-luminosity systems
in comparison to the field, although it is not yet agreed whether this effect
is the result of initial galaxy mass functions that vary with environment or
galaxy evolutionary effects. In this letter we argue that this over-density is
the result of low-mass systems with red colors that are over-populating the
faint-end of the observed luminosity function in the nearby rich cluster Abell
0426. We show that the luminosity function of Abell 0426 becomes steeper, from
the field value alpha = -1.25+/-0.05 to alpha=-1.44+/-0.04, due to a recently
identified population of red low-mass cluster galaxies that are possibly the
remnants of dynamical stripped high-mass systems. We further demonstrate,
through simple models of stripping effects, how cluster luminosity functions
can become artificially steep over time from the production of these low-mass
cluster galaxies.Comment: Accepted to ApJ letter
Asymmetry measures for QSOs and companions
An asymmetry index is derived from ellipse-fitting to galaxy images, that
gives weight to faint outer features and is not strongly redshift-dependent.
These measures are made on a sample of 13 2MASS QSOs and their neighbour
galaxies, and a control sample of field galaxies from the same wide-field
imaging data. The QSO host galaxy asymmetries correlate well with visual tidal
interaction indices previously published. The companion galaxies have somewhat
higher asymmetry than the control galaxy sample, and their asymmetry is
inversely correlated with distance from the QSO. The distribution of
QSO-companion asymmetry indices is different from that for matched control
field galaxies at the significance level. We present the data and
discuss this evidence for tidal and other disturbances in the vicinity of QSOs.Comment: 13 pages, 2 tables, 4 figures; to appear in A
Exploring the evolutionary paths of the most massive galaxies since z~2
We use Spitzer MIPS data from the FIDEL Legacy Project in the Extended Groth
Strip to analyze the stellar mass assembly of massive (M>10^11 M_sun) galaxies
at z<2 as a function of structural parameters. We find 24 micron emission for
more than 85% of the massive galaxies morphologically classified as disks, and
for more than 57% of the massive systems morphologically classified as
spheroids at any redshift, with about 8% of sources harboring a bright X-ray
and/or infrared emitting AGN. More noticeably, 60% of all compact massive
galaxies at z=1-2 are detected at 24 micron, even when rest-frame optical
colors reveal that they are dead and evolving passively. For spheroid-like
galaxies at a given stellar mass, the sizes of MIPS non-detections are smaller
by a factor of 1.2 in comparison with IR-bright sources. We find that disk-like
massive galaxies present specific SFRs ranging from 0.04 to 0.2 Gyr^-1 at z<1
(SFRs ranging from 1 to 10 M_sun/yr), typically a factor of 3-6 higher than
massive spheroid-like objects in the same redshift range. At z>1, and more
pronouncedly at z>1.3, the median specific SFRs of the disks and spheroids
detected by MIPS are very similar, ranging from 0.1 to 1 Gyr^-1 (SFR=10-200
M_sun/yr). We estimate that massive spheroid-like galaxies may have doubled (at
the most) their stellar mass from star-forming events at z<2: less than 20%
mass increase at 1.7<z<2.0, up to 40% more at 1.1<z<1.7, and less than 20%
additional increase at z<1. Disk-like galaxies may have tripled (at the most)
their stellar mass at z<2 from star formation alone: up to 40% mass increase at
1.7<z<2.0, and less than 180% additional increase below z=1.7 occurred at a
steady rate.Comment: Accepted for publication in ApJ; 10 pages, 5 figures, 1 tabl
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