58 research outputs found
IR observations of MS 1054-03: Star Formation and its Evolution in Rich Galaxy Clusters
We study the infrared (IR) properties of galaxies in the cluster MS 1054-03
at z=0.83 by combining MIPS 24 micron data with spectra of more than 400
galaxies and a very deep K-band selected catalog. 19 IR cluster members are
selected spectroscopically, and an additional 15 are selected by their
photometric redshifts. We derive the IR luminosity function of the cluster and
find strong evolution compared to the similar-mass Coma cluster. The best
fitting Schechter function gives L*_{IR}=11.49 +0.30/-0.29 L_sun with a fixed
faint end slope, about one order of magnitude larger than that in Coma. The
rate of evolution of the IR luminosity from Coma to MS 1054-03 is consistent
with that found in field galaxies, and it suggests that some internal
mechanism, e.g., the consumption of the gas fuel, is responsible for the
general decline of the cosmic star formation rate (SFR) in different
environments. The mass-normalized integrated SFR within 0.5R_200 in MS 1054-03
also shows evolution compared with other rich clusters at lower redshifts, but
the trend is less conclusive if the mass selection effect is considered. A
nonnegligible fraction (13%) of cluster members, are forming stars actively and
the overdensity of IR galaxies is about 20 compared to the field. It is
unlikely that clusters only passively accrete star forming galaxies from the
surrounding fields and have their star formation quenched quickly afterward;
instead, many cluster galaxies still have large amounts of gas, and their star
formation may be enhanced by the interaction with the cluster.Comment: 49 pages, 9 figures, accepted by Ap
Infrared Luminosity Function of the Coma Cluster
Using mid-IR and optical data, we deduce the total infrared (IR) luminosities
of galaxies in the Coma cluster and present their infrared luminosity function
(LF). The shape of the overall Coma IR LF does not show significant differences
from the IR LFs of the general field, which indicates the general independence
of global galaxy star formation on environment up to densities 40 times
greater than in the field (we cannot test such independence above ). However, a shallower faint end slope and a
smaller are found in the core region (where the densities are
still higher) compared to the outskirt region of the cluster, and most of the
brightest IR galaxies are found outside of the core region. The IR LF in the
NGC 4839 group region does not show any unique characteristics. By integrating
the IR LF, we find a total star formation rate in the cluster of about 97.0
M_{\sun}{\rm yr}^{-1}. We also studied the contributions of early- and
late-type galaxies to the IR LF. The late-type galaxies dominate the bright end
of the LF, and the early-type galaxies, although only making up a small portion
( 15%) of the total IR emission of the cluster, contribute greatly to
the number counts of the LF at .Comment: 33 pages, 8 figures, 1 table. Accepted for publication in The
Astrophysical Journa
RCS2 J232727.6-020437: An Efficient Cosmic Telescope at
We present a detailed gravitational lens model of the galaxy cluster RCS2
J232727.6-020437. Due to cosmological dimming of cluster members and ICL, its
high redshift () makes it ideal for studying background galaxies.
Using new ACS and WFC3/IR HST data, we identify 16 multiple images. From
MOSFIRE follow up, we identify a strong emission line in the spectrum of one
multiple image, likely confirming the redshift of that system to .
With a highly magnified () source plane area of
arcmin at , RCS2 J232727.6-020437 has a lensing efficiency comparable
to the Hubble Frontier Fields clusters. We discover four highly magnified
candidate Lyman-break galaxies behind the cluster, one of which may be
multiply-imaged. Correcting for magnification, we find that all four galaxies
are fainter than . One candidate is detected at in
both Spitzer/IRAC [3.6] and [4.5] channels. A spectroscopic follow-up with
MOSFIRE does not result in the detection of the Lyman-alpha emission line from
any of the four candidates. From the MOSFIRE spectra we place median upper
limits on the Lyman-alpha flux of ().Comment: 14 pages, 9 figures, submitted to ApJ on 3/06/201
The Thick Disk in the Galaxy NGC 4244 from S^4G Imaging
If thick disks are ubiquitous and a natural product of disk galaxy formation and/or evolution processes, all
undisturbed galaxies that have evolved during a significant fraction of a Hubble time should have a thick disk. The
late-type spiral galaxy NGC 4244 has been reported as the only nearby edge-on galaxy without a confirmed thick
disk. Using data from the Spitzer Survey of Stellar Structure in Galaxies (S^4G) we have identified signs of two disk
components in this galaxy. The asymmetries between the light profiles on both sides of the mid-plane of NGC 4244
can be explained by a combination of the galaxy not being perfectly edge-on and a certain degree of opacity of
the thin disk. We argue that the subtlety of the thick disk is a consequence of either a limited secular evolution in
NGC 4244, a small fraction of stellar material in the fragments which built the galaxy, or a high amount of gaseous
accretion after the formation of the galaxy
Mid-infrared Galaxy Morphology from the Spitzer Survey of Stellar Structure in Galaxies (S^4G): The Imprint of the De Vaucouleurs Revised Hubble-Sandage Classification System at 3.6 μm
Spitzer Space Telescope Infrared Array Camera imaging provides an opportunity to study all known morphological types of galaxies in the mid-IR at a depth significantly better than ground-based near-infrared and optical images. The goal of this study is to examine the imprint of the de Vaucouleurs classification volume in the 3.6 μm band, which is the best Spitzer waveband for galactic stellar mass morphology owing to its depth and its reddening-free sensitivity mainly to older stars. For this purpose, we have prepared classification images for 207 galaxies from the Spitzer archive, most of which are formally part of the Spitzer Survey of Stellar Structure in Galaxies (S^4G), a Spitzer post-cryogenic ("warm") mission Exploration Science Legacy Program survey of 2331 galaxies closer than 40 Mpc. For the purposes of morphology, the galaxies are interpreted as if the images are blue light, the historical waveband for classical galaxy classification studies. We find that 3.6 μm classifications are well correlated with blue-light classifications, to the point where the essential features of many galaxies look very similar in the two very different wavelength regimes. Drastic differences are found only for the most dusty galaxies. Consistent with a previous study by Eskridge et al., the main difference between blue-light and mid-IR types is an ≈1 stage interval difference for S0/a to Sbc or Sc galaxies, which tend to appear "earlier" in type at 3.6 μm due to the slightly increased prominence of the bulge, the reduced effects of extinction, and the reduced (but not completely eliminated) effect of the extreme population I stellar component. We present an atlas of all of the 207 galaxies analyzed here and bring attention to special features or galaxy types, such as nuclear rings, pseudobulges, flocculent spiral galaxies, I0 galaxies, double-stage and double-variety galaxies, and outer rings, that are particularly distinctive in the mid-IR
Metal Abundances of KISS Galaxies. IV. Galaxian Luminosity-Metallicity Relations in the Optical and Near-IR
We explore the galaxian luminosity-metallicity (L-Z) relationship in both the
optical and the near-IR using a combination of optical photometric and
spectroscopic observations from the KPNO International Spectroscopic Survey
(KISS) and near-infrared photometry from the Two-micron All Sky Survey (2MASS).
We supplement the 2MASS data with our own NIR photometry for a small number of
lower-luminosity ELGs that are under-represented in the 2MASS database. Our
B-band L-Z relationship includes 765 star-forming KISS galaxies with coarse
abundance estimates from our follow-up spectra, while the correlation with KISS
and 2MASS yields a total of 420 galaxies in our J-band L-Z relationship. We
explore the effect that changing the correlation between the strong-line
abundance diagnostic R_23 and metallicity has on the derived L-Z relation. We
find that the slope of the L-Z relationship decreases as the wavelength of the
luminosity bandpass increases. We interpret this as being, at least in part, an
effect of internal absorption in the host galaxy. Furthermore, the dispersion
in the L-Z relation decreases for the NIR bands, suggesting that variations in
internal absorption contribute significantly to the observed scatter. We
propose that our NIR L-Z relations are more fundamental than the B-band
relation, since they are largely free of absorption effects and the NIR
luminosities are more directly related to the stellar mass of the galaxy than
are the optical luminosities.Comment: 22 pages, including 6 figures and 6 tables. Accepted for publication
in the Astrophysical Journal (20 May 2005 issue
24 MICRON PROPERTIES OF X-RAY-SELECTED ACTIVE GALACTIC NUCLEI
We examine the 24 μm to X-ray color of 157 X-ray-selected active galactic nuclei (AGNs) as a function of X-ray obscuration and optical classification in the Chandra Deep Field-South. The sample consists of the Chandra hard-band detections with 2-8 keV flux above 10-15 ergs s-1 cm-2. A deep 24 μm mosaic obtained with Spitzer provides mid-infrared fluxes for the sample. Since obscured AGNs locally have higher 24 μm/2-8 keV flux ratios than unobscured AGNs, and since X-ray background models predict a large population of obscured AGNs, we expect to find many X-ray-hard, IR-bright AGNs. Instead, we find that the 24 μm to X-ray flux ratio does not depend on X-ray hardness in the full sample, nor does it differ between narrow- and broad-line AGNs. We identify five nearly Compton-thick AGNs and find they have similar 24 μm to X-ray flux ratios compared to the full sample. We consider AGNs in the narrow redshift spikes at z ~ 0.7; for these AGNs, there is some evidence that the flux ratio increases with X-ray hardness. The redshift slice also shows an odd trend that is also prominent in the full sample: a group of X-ray-hard AGNs with very low 24 μm to X-ray flux ratios
The Spitzer Survey of Stellar Structure in Galaxies (S^4G)
The Spitzer Survey of Stellar Structure in Galaxies S^4G is an Exploration
Science Legacy Program approved for the Spitzer post-cryogenic mission. It is a
volume-, magnitude-, and size-limited (d < 40 Mpc, |b| > 30 degrees, m_(Bcorr)
< 15.5, D25>1') survey of 2,331 galaxies using IRAC at 3.6 and 4.5 microns.
Each galaxy is observed for 240 s and mapped to > 1.5 x D25. The final
mosaicked images have a typical 1 sigma rms noise level of 0.0072 and 0.0093
MJy / sr at 3.6 and 4.5 microns, respectively. Our azimuthally-averaged surface
brightness profile typically traces isophotes at mu_3.6 (AB) (1 sigma) ~ 27 mag
arcsec^-2, equivalent to a stellar mass surface density of ~ 1 Msun pc^-2. S^4G
thus provides an unprecedented data set for the study of the distribution of
mass and stellar structures in the local Universe. This paper introduces the
survey, the data analysis pipeline and measurements for a first set of
galaxies, observed in both the cryogenic and warm mission phase of Spitzer. For
every galaxy we tabulate the galaxy diameter, position angle, axial ratio,
inclination at mu_3.6 (AB) = 25.5 and 26.5 mag arcsec^-2 (equivalent to ~ mu_B
(AB) =27.2 and 28.2 mag arcsec^-2, respectively). These measurements will form
the initial S^4G catalog of galaxy properties. We also measure the total
magnitude and the azimuthally-averaged radial profiles of ellipticity, position
angle, surface brightness and color. Finally, we deconstruct each galaxy using
GALFIT into its main constituent stellar components: the bulge/spheroid, disk,
bar, and nuclear point source, where necessary. Together these data products
will provide a comprehensive and definitive catalog of stellar structures, mass
and properties of galaxies in the nearby Universe.Comment: Accepted for Publication in PASP, 14 pages, 13 figure
Understanding Radio-Selected Thermal Sources in M 33: Ultraviolet, Optical, Near-Infrared, Spitzer Mid-Infrared, and Radio Observations
We present ultraviolet, optical, near-infrared, Spitzer mid-infrared, and
radio images of 14 radio-selected objects in M 33. These objects are thought to
represent the youngest phase of star cluster formation. We have detected the
majority of cluster candidates in M 33 at all wavelengths. From the near-IR
images, we derived ages 2-10 Myr, K_S-band extinctions (A_K_S) of 0-1 mag, and
stellar masses of 10^3-10^4 M_solar. We have generated spectral energy
distributions (SEDs) of each cluster from 0.1 micron to 160 microns. From these
SEDs, we have modeled the dust emission around these star clusters to determine
the dust masses (1-10^3 M_solar) and temperatures (40-90 K) of the clusters'
local interstellar medium. Extinctions derived from the JHK_S, Halpha, and UV
images are similar to within a factor of 2 or 3. These results suggest that
eleven of the fourteen radio-selected objects are optically-visible young star
clusters with a surrounding H II region, that two are background objects,
possibly AGN, and that one is a Wolf-Rayet star with a surrounding H II region.Comment: 57 pages total; 20 figures; 3 tables under review by ApJS; first
review complet
Grand Design and Flocculent Spirals in the Spitzer Survey of Stellar Structure in Galaxies (S4G)
Spiral arm properties of 46 galaxies in the Spitzer Survey of Stellar
Structure in Galaxies (S4G) were measured at 3.6mu, where extinction is small
and the old stars dominate. The sample includes flocculent, multiple arm, and
grand design types with a wide range of Hubble and bar types. We find that most
optically flocculent galaxies are also flocculent in the mid-IR because of star
formation uncorrelated with stellar density waves, whereas multiple arm and
grand design galaxies have underlying stellar waves. Arm-interarm contrasts
increase from flocculent to multiple arm to grand design galaxies and with
later Hubble types. Structure can be traced further out in the disk than in
previous surveys. Some spirals peak at mid-radius while others continuously
rise or fall, depending on Hubble and bar type. We find evidence for regular
and symmetric modulations of the arm strength in NGC 4321. Bars tend to be
long, high amplitude, and flat-profiled in early type spirals, with arm
contrasts that decrease with radius beyond the end of the bar, and they tend to
be short, low amplitude, and exponential-profiled in late Hubble types, with
arm contrasts that are constant or increase with radius. Longer bars tend to
have larger amplitudes and stronger arms.Comment: 31 pages, 14 figures, ApJ in pres
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