167 research outputs found
On the Classification of UGC1382 as a Giant Low Surface Brightness Galaxy
We provide evidence that UGC1382, long believed to be a passive elliptical
galaxy, is actually a giant low surface brightness (GLSB) galaxy which rivals
the archetypical GLSB Malin 1 in size. Like other GLSB galaxies, it has two
components: a high surface brightness disk galaxy surrounded by an extended low
surface brightness (LSB) disk. For UGC1382, the central component is a
lenticular system with an effective radius of 6 kpc. Beyond this, the LSB disk
has an effective radius of ~38 kpc and an extrapolated central surface
brightness of ~26 mag/arcsec^2. Both components have a combined stellar mass of
~8x10^10 M_sun, and are embedded in a massive (10^10 M_sun) low-density (<3
M_sun/pc^2) HI disk with a radius of 110 kpc, making this one of the largest
isolated disk galaxies known. The system resides in a massive dark matter halo
of at least 2x10^12 M_sun. Although possibly part of a small group, its low
density environment likely plays a role in the formation and retention of the
giant LSB and HI disks. We model the spectral energy distributions and find
that the LSB disk is likely older than the lenticular component. UGC1382 has
UV-optical colors typical of galaxies transitioning through the green valley.
Within the LSB disk are spiral arms forming stars at extremely low
efficiencies. The gas depletion time scale of ~10^11 yr suggests that UGC1382
may be a very long term resident of the green valley. We find that the
formation and evolution of the LSB disk is best explained by the accretion of
gas-rich LSB dwarf galaxies.Comment: 17 pages, 16 figures, 4 tables; accepted to the Astrophysical Journa
CNN photometric redshifts in the SDSS at
We release photometric redshifts, reaching 0.7, for 14M galaxies
at in the 11,500 deg of the SDSS north and south galactic caps.
These estimates were inferred from a convolution neural network (CNN) trained
on stamp images of galaxies labelled with a spectroscopic redshift from
the SDSS, GAMA and BOSS surveys. Representative training sets of 370k
galaxies were constructed from the much larger combined spectroscopic data to
limit biases, particularly those arising from the over-representation of
Luminous Red Galaxies. The CNN outputs a redshift classification that offers
all the benefits of a well-behaved PDF, with a width efficiently signaling
unreliable estimates due to poor photometry or stellar sources. The dispersion,
mean bias and rate of catastrophic failures of the median point estimate are of
order , , on a representative test sample at ,
out-performing currently published estimates. The distributions in narrow
intervals of magnitudes of the redshifts inferred for the photometric sample
are in good agreement with the results of tomographic analyses. The inferred
redshifts also match the photometric redshifts of the redMaPPer galaxy clusters
for the probable cluster members. The CNN input and output are available at:
https://deepdip.iap.fr/treyer+2023.Comment: Submitted to MNRA
The Space Density of Extended Ultraviolet (XUV) Disks in the Local Universe and Implications for Gas Accretion on to Galaxies
We present results of the first unbiased search for extended UV (XUV)-disk
galaxies undertaken to determine the space density of such galaxies. Our sample
contains 561 local (0.001 < z < 0.05) galaxies that lie in the intersection of
available GALEX deep imaging (exposure time > 1.5 x 10^4 s) and SDSS DR7
footprints. We explore modifications to the standard classification scheme for
our sample that includes both disk- and bulge-dominated galaxies. Visual
classification of each galaxy in the sample reveals an XUV-disk frequency of up
to 20% for the most nearby portion of our sample. On average over the entire
sample (out to z=0.05) the frequency ranges from a hard limit of 4% to 14%. The
GALEX imaging allows us to detect XUV-disks beyond 100 Mpc. The XUV regions
around XUV-disk galaxies are consistently bluer than the main bodies. We find a
surprisingly high frequency of XUV emission around luminous red (NUV-r > 5) and
green valley (3 < NUV-r < 5) galaxies. The XUV-disk space density in the local
universe is > 1.5-4.2 x 10^-3 Mpc^-3. Using the XUV emission as an indicator of
recent gas accretion, we estimate that the cold gas accretion rate onto these
galaxies is > 1.7-4.6 x 10^-3 Msun Mpc^-3 yr^-1. The number of XUV-disks in the
green valley and the estimated accretion rate onto such galaxies points to the
intriguing possibility that 7%-18% of galaxies in this population are
transitioning away from the red sequence.Comment: 19 pages, 24 figures, ApJ in Pres
The VIPERS Multi-Lambda Survey. I. UV and NIR Observations, multi-color catalogues and photometric redshifts
We present observations collected in the CFHTLS-VIPERS region in the
ultraviolet (UV) with the GALEX satellite (far and near UV channels) and the
near infrared with the CFHT/WIRCam camera (-band) over an area of 22 and
27 deg, respectively. The depth of the photometry was optimized to measure
the physical properties (e.g., SFR, stellar masses) of all the galaxies in the
VIPERS spectroscopic survey. The large volume explored by VIPERS will enable a
unique investigation of the relationship between the galaxy properties and
their environment (density field and cosmic web) at high redshift (0.5 < z <
1.2). In this paper, we present the observations, the data reductions and the
build-up of the multi-color catalogues. The CFHTLS-T0007 (gri-{\chi}^2) images
are used as reference to detect and measure the -band photometry, while
the T0007 u-selected sources are used as priors to perform the GALEX photometry
based on a dedicated software (EMphot). Our final sample reaches ~25
(at 5{\sigma}) and ~22 (at 3{\sigma}). The large spectroscopic sample
(~51,000 spectroscopic redshifts) allows us to highlight the robustness of our
star/galaxy separation, and the reliability of our photometric redshifts with a
typical accuracy 0.04 and a catastrophic failure rate {\eta} <
2% down to i~23. We present various tests on the band completeness and
photometric redshift accuracy by comparing with existing, overlapping deep
photometric catalogues. Finally, we discuss the BzK sample of passive and
active galaxies at high redshift and the evolution of galaxy morphology in the
(NUV-r) vs (r-K_s) diagram at low redshift (z < 0.25) thanks to the high image
quality of the CFHTLS. The images, catalogues and photometric redshifts for 1.5
million sources (down to 25 or 22) are released and
available at this URL: http://cesam.lam.fr/vipers-mls/Comment: 14 pages, 16 figures. Accepted for publication in A&A. Version to be
publishe
SSGSS: The Spitzer-SDSS-GALEX Spectroscopic Survey
The Spitzer-SDSS-GALEX Spectroscopic Survey (SSGSS) provides a new sample of
101 star-forming galaxies at z < 0.2 with unprecedented multi-wavelength
coverage. New mid- to far-infrared spectroscopy from the Spitzer Space
Telescope is added to a rich suite of previous imaging and spectroscopy,
including ROSAT, Galaxy Evolution Explorer, Sloan Digital Sky Survey, Two
Micron All Sky Survey, and Spitzer/SWIRE. Sample selection ensures an even
coverage of the full range of normal galaxy properties, spanning two orders of
magnitude in stellar mass, color, and dust attenuation. In this paper we
present the SSGSS data set, describe the science drivers, and detail the sample
selection, observations, data reduction, and quality assessment. Also in this
paper, we compare the shape of the thermal continuum and the degree of silicate
absorption of these typical, star-forming galaxies to those of starburst
galaxies. We investigate the link between star formation rate, infrared
luminosity, and total polycyclic aromatic hydrocarbon luminosity, with a view
to calibrating the latter for spectral energy distribution models in
photometric samples and at high redshift. Last, we take advantage of the 5-40
micron spectroscopic and far-infrared photometric coverage of this sample to
perform detailed fitting of the Draine et al. dust models, and investigate the
link between dust mass and star formation history and active galactic nucleus
properties.Comment: 60 pages, 20 figure
New Constraint on Open Cold-Dark-Matter Models
We calculate the large-angle cross-correlation between the
cosmic-microwave-background (CMB) temperature and the x-ray-background (XRB)
intensity expected in an open Universe with cold dark matter (CDM) and a nearly
scale-invariant spectrum of adiabatic density perturbations. Results are
presented as a function of the nonrelativistic-matter density (in
units of the critical density) and the x-ray bias (evaluated at a
redshift in evolving-bias models) for both an open Universe and a
flat cosmological-constant Universe. Recent experimental upper limits to the
amplitude of this cross-correlation provide a new constraint to the
- parameter space that open-CDM models (and the open-inflation
models that produce them) must satisfy.Comment: 4 pages, LaTeX. Revised version contains additional figure that
clarifies new constraint. (To appear in PRL.
Mid-Infrared Spectral Measures of Star-Formation and AGN Activity in Normal Galaxies
We investigate the use of MIR PAH bands, continuum and emission lines as
probes of star-formation and AGN activity in a sample of 100 'normal' and local
(z~0.1) emission-line galaxies. The MIR spectra were obtained with the Spitzer
Space Telescope Infrared Spectrograph (IRS) as part of the Spitzer-SDSS-GALEX
Spectroscopic Survey (SSGSS) which includes multi-wavelength photometry from
the UV to the FIR and optical spectroscopy. The continuum and features were
extracted using PAHFIT (Smith et al. 2007), a decomposition code which we find
to yield PAH equivalent widths up to ~30 times larger than the commonly used
spline methods. Despite the lack of extreme objects in our sample (such as
strong AGNs, low metallicity galaxies or ULIRGs), we find significant
variations in PAH, continuum and emission line properties and systematic trends
between these MIR properties and optically derived physical properties such as
age, metallicity and radiation field hardness. We revisit the diagnostic
diagram relating PAH equivalent widths and [Ne II]12.8micrometers/[O
IV]25.9micrometers line ratios and find it to be in much better agreement with
the standard optical star-formation/AGN classification than when spline
decompositions are used, while also potentially revealing obscured AGNs. The
luminosity of individual PAH components, of the continuum, and with poorer
statistics, of the neon emission lines and molecular hydrogen lines, are found
to be tightly correlated to the total IR luminosity, making individual MIR
components good gauges of the total dust emission in SF galaxies. Like the
total IR luminosity, these individual components can be used to estimate dust
attenuation in the UV and in Halpha lines based on energy balance arguments. We
also propose average scaling relations between these components and dust
corrected, Halpha derived star-formation rates.Comment: Accepted for publication in Ap
The GALEX UV luminosity function of the cluster of galaxies Abell 1367
We present the GALEX NUV (2310 A) and FUV (1530 A) galaxy luminosity
functions of the nearby cluster of galaxies A1367 in the magnitude range -20.3<
M_AB < -13.3. The luminosity functions are consistent with previous (~ 2 mag
shallower) estimates based on the FOCA and FAUST experiments, but display a
steeper faint-end slope than the GALEX luminosity function for local field
galaxies. Using spectro-photometric optical data we select out star-forming
systems from quiescent galaxies and study their separate contributions to the
cluster luminosity function. We find that the UV luminosity function of cluster
star-forming galaxies is consistent with the field. The difference between the
cluster and field LF is entirely due to the contribution at low luminosities
(M_AB >-16 mag) of non star-forming, early-type galaxies that are significantly
over dense in clusters.Comment: 4 pages, 4 figures, 1 table. Accepted for publication in
Astrophysical Journal Letter
The UV-Optical Galaxy Color-Magnitude Diagram. I. Basic Properties
We have analyzed the bivariate distribution of galaxies as a function of ultraviolet-optical colors and absolute magnitudes in the local universe. The sample consists of galaxies with redshifts and optical photometry from the Sloan Digital Sky Survey (SDSS) main galaxy sample matched with detections in the near-ultraviolet (NUV) and far-ultraviolet (FUV) bands in the Medium Imaging Survey being carried out by the Galaxy Evolution Explorer (GALEX) satellite. In the (NUV − r)_(0.1) versus M_(r,0.1) galaxy color-magnitude diagram, the galaxies separate into two well-defined blue and red sequences. The (NUV − r)_(0.1) color distribution at each M_(r,0.1) is not well fit by the sum of two Gaussians due to an excess of galaxies in between the two sequences. The peaks of both sequences become redder with increasing luminosity, with a distinct blue peak visible up to M_(r,0.1) ~ − 23. The r_(0.1)-band luminosity functions vary systematically with color, with the faint-end slope and characteristic luminosity gradually increasing with color. After correcting for attenuation due to dust, we find that approximately one-quarter of the color variation along the blue sequence is due to dust, with the remainder due to star formation history and metallicity. Finally, we present the distribution of galaxies as a function of specific star formation rate and stellar mass. The specific star formation rates imply that galaxies along the blue sequence progress from low-mass galaxies with star formation rates that increase somewhat with time to more massive galaxies with a more or less constant star formation rate. Above a stellar mass of ~10^(10.5) M_☉, galaxies with low ratios of current to past averaged star formation rate begin to dominate
The Star Formation Rate Density and Dust Attenuation Evolution over 12 Gyr with the VVDS Surveys
[Abridged] We investigate the global galaxy evolution over 12 Gyr
(0.05<z<4.5), from the star formation rate density (SFRD), combining the VVDS
Deep (17.5<=I<=24.0) and Ultra-Deep (23.00<=i<=24.75) surveys. We obtain a
single homogeneous spectroscopic redshift sample, totalizing about 11000
galaxies. We estimate the rest-frame FUV luminosity function (LF) and
luminosity density (LD), extract the dust attenuation of the FUV radiation
using SED fitting, and derive the dust-corrected SFRD. We find a constant and
flat faint-end slope alpha in the FUV LF at z1.7, we set alpha
steepening with (1+z). The absolute magnitude M*_FUV brightens in the entire
range 02 it is on average brighter than in the literature,
while phi* is smaller. Our total LD shows a peak at z=2, present also when
considering all sources of uncertainty. The SFRD history peaks as well at z=2.
It rises by a factor of 6 during 2 Gyr (from z=4.5 to z=2), and then decreases
by a factor of 12 during 10 Gyr down to z=0.05. This peak is mainly produced by
a similar peak within the population of galaxies with -21.5<=M_FUV<=-19.5 mag.
As times goes by, the total SFRD is dominated by fainter and fainter galaxies.
The presence of a clear peak at z=2 and a fast rise at z>2 of the SFRD is
compelling for models of galaxy formation. The mean dust attenuation A_FUV of
the global galaxy population rises by 1 mag during 2 Gyr from z=4.5 to z=2,
reaches its maximum at z=1 (A_FUV=2.2 mag), and then decreases by 1.1 mag
during 7 Gyr down to z=0. The dust attenuation maximum is reached 2 Gyr after
the SFRD peak, implying a contribution from the intermediate-mass stars to the
dust production at z<2.Comment: 23 pages, 15 figures, accepted for publication in A&
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