48 research outputs found
Early-Type Galaxies in the Hubble Deep Field: The Star Formation History
We have investigated the properties of a complete K-band selected sample of 35 elliptical and S0 galaxies brighter than K=20.15 in the Hubble Deep Field, as representative of the field galaxy population. This sample has been derived from deep K-band image by the KPNO-IRIM camera, by applying a rigorous morphological classification scheme based on quantitative analyses of the surface brightness profiles. The broad-band spectra of the sample galaxies allow us to date their dominant stellar populations. The majority of bright early-types in this field are found at redshifts z<1.3 to display colors indicative of a fairly wide range of ages (typically 1.5 to 3 Gyrs). We find that the major episodes of star-formation building up typical M_star galaxies have taken place during a wide redshift interval 11.3, which should be detectable during the luminous star-formation phase expected to happen at these redshifts. Obvious solutions are a) that the merging events imply perturbed morphologies which prevent selecting them by our morphological classification filter, or b) that a dust-polluted ISM obscures the (either continuous or episodic) events of star-formation. We conclude that the likely solution is a combination thereof, i.e. a set of dust-enshrouded merging-driven starbursts occurring during the first few Gyrs of the galaxy's lifetime
The EFIGI catalogue of 4458 nearby galaxies with detailed morphology
Accepted for publication in Astronomy and Astrophysics, 27 pages, 7 tables, 32 colour figures. Data available at http://www.efigi.orgInternational audienceNow that large databases of resolved galaxy images are provided by modern imaging surveys, advanced morphological studies can be envisioned, urging for well defined calibration samples. We present the EFIGI catalogue, a multiwavelength database specifically designed for a dense sampling of all Hubble types. The catalogue merges data from standard surveys and catalogues (Principal Galaxy Catalogue, Sloan Digital Sky Survey, Value-Added Galaxy Catalogue, HyperLeda, and the NASA Extragalactic Database) and provides detailed morphological information. Imaging data are obtained from the SDSS DR4 in the u, g, r, i, and z bands for a sample of 4458 PGC galaxies, whereas photometric and spectroscopic data are obtained from the SDSS DR5 catalogue. Point-Spread Function models are derived in all five bands. Composite colour images of all objects are visually examined by a group of astronomers, and galaxies are staged along the Hubble sequence and classified according to 16 morphological attributes describing their structure, texture, as well as environment and appearance on a five-level scale. The EFIGI Hubble sequence shows remarkable agreement with the RC3 Revised Hubble Sequence. The main characteristics and reliability of the catalogue are examined, including photometric completeness, type mix, systematic trends and correlations. The final EFIGI database is a large sub-sample of the local Universe, with a dense sampling of Sd, Sdm, Sm and Im types compared to magnitude-limited catalogues. We estimate the photometric catalogue to be more than ~ 80% complete for galaxies with 10 < g < 14. More than 99.5% of EFIGI galaxies have a known redshift in the HyperLeda and NED databases
Post-starburst galaxies: more than just an interesting curiosity
From the VIMOS VLT DEEP Survey (VVDS) we select a sample of 16 galaxies with
spectra which identify them as having recently undergone a strong starburst and
subsequent fast quenching of star formation. These post-starburst galaxies lie
in the redshift range 0.510^9.75Msun. They have a number
density of 1x10^-4 per Mpc^3, almost two orders of magnitude sparser than the
full galaxy population with the same mass limit. We compare with simulations to
show that the galaxies are consistent with being the descendants of gas rich
major mergers. Starburst mass fractions must be larger than ~5-10% and decay
times shorter than ~10^8 years for post-starburst spectral signatures to be
observed in the simulations. We find that the presence of black hole feedback
does not greatly affect the evolution of the simulated merger remnants through
the post-starburst phase. The multiwavelength spectral energy distributions of
the post-starburst galaxies show that 5/16 have completely ceased the formation
of new stars. These 5 galaxies correspond to a mass flux entering the
red-sequence of rhodot(A->Q, PSB) = 0.0038Msun/Mpc^3/yr, assuming the defining
spectroscopic features are detectable for 0.35Gyr. If the galaxies subsequently
remain on the red sequence, this accounts for 38(+4/-11)% of the growth rate of
the red sequence. Finally, we compare our high redshift results with a sample
of galaxies with 0.05<z<0.1 observed in the SDSS and UKIDSS surveys. We find a
very strong redshift evolution: the mass density of strong post-starburst
galaxies is 230 times lower at z~0.07 than at z~0.7.Comment: 18 pages, 12 figures, to match version accepted to MNRAS. Minor
reordering of text in places and Sec 2.2 on SPH simulation comparisons
expande
The UV-Optical Color Dependence of Galaxy Clustering in the Local Universe
We measure the UV-optical color dependence of galaxy clustering in the local
universe. Using the clean separation of the red and blue sequences made
possible by the NUV - r color-magnitude diagram, we segregate the galaxies into
red, blue and intermediate "green" classes. We explore the clustering as a
function of this segregation by removing the dependence on luminosity and by
excluding edge-on galaxies as a means of a non-model dependent veto of highly
extincted galaxies. We find that \xi (r_p, \pi) for both red and green galaxies
shows strong redshift space distortion on small scales -- the "finger-of-God"
effect, with green galaxies having a lower amplitude than is seen for the red
sequence, and the blue sequence showing almost no distortion. On large scales,
\xi (r_p, \pi) for all three samples show the effect of large-scale streaming
from coherent infall. On scales 1 Mpc/h < r_p < 10 Mpc/h, the projected
auto-correlation function w_p(r_p) for red and green galaxies fits a power-law
with slope \gamma ~ 1.93 and amplitude r_0 ~ 7.5 and 5.3, compared with \gamma
~ 1.75 and r_0 ~ 3.9 Mpc/h for blue sequence galaxies. Compared to the
clustering of a fiducial L* galaxy, the red, green, and blue have a relative
bias of 1.5, 1.1, and 0.9 respectively. The w_p(r_p) for blue galaxies display
an increase in convexity at ~ 1 Mpc/h, with an excess of large scale
clustering. Our results suggest that the majority of blue galaxies are likely
central galaxies in less massive halos, while red and green galaxies have
larger satellite fractions, and preferentially reside in virialized structures.
If blue sequence galaxies migrate to the red sequence via processes like
mergers or quenching that take them through the green valley, such a
transformation may be accompanied by a change in environment in addition to any
change in luminosity and color.Comment: accepted by MNRA
The UV Galaxy Luminosity Function in the Local Universe from GALEX Data
We present the results of a determination of the galaxy luminosity function
at ultraviolet wavelengths at redshifts of from GALEX data. We
determined the luminosity function in the GALEX FUV and NUV bands from a sample
of galaxies with UV magnitudes between 17 and 20 that are drawn from a total of
56.73 deg^2 of GALEX fields overlapping the b_j-selected 2dF Galaxy Redshift
Survey. The resulting luminosity functions are fainter than previous UV
estimates and result in total UV luminosity densities of 10^(25.55+/-0.12) ergs
s^-1 Hz^-1 Mpc^-3 and 10^(25.72+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 at 1530 Ang. and
2310 Ang., respectively. This corresponds to a local star formation rate
density in agreement with previous estimates made with H-alpha-selected data
for reasonable assumptions about the UV extinction.Comment: This paper will be published as part of the Galaxy Evolution Explorer
(GALEX) Astrophysical Journal Letters Special Issue. Links to the full set of
papers will be available at http://www.galex.caltech.edu/PUBLICATIONS/ after
November 22, 200
PRIMUS: Enhanced Specific Star Formation Rates In Close Galaxy Pairs
Tidal interactions between galaxies can trigger star formation, which
contributes to the global star formation rate density of the universe and could
be a factor in the transformation of blue, star-forming galaxies to red,
quiescent galaxies over cosmic time. We investigate tidally-triggered star
formation in isolated close galaxy pairs drawn from the Prism Multi-Object
Survey (PRIMUS), a low-dispersion prism redshift survey that has measured
~120,000 robust galaxy redshifts over 9.1 deg^2 out to z ~ 1. We select a
sample of galaxies in isolated galaxy pairs at redshifts 0.25 < z < 0.75, with
no other objects within a projected separation of 300 h^-1 kpc and dz/(1+z) =
0.01, and compare them to a control sample of isolated galaxies to test for
systematic differences in their rest-frame FUV-r and NUV-r colors as a proxy
for relative specific SFR. We find that galaxies in r_p < 50 h^-1 kpc pairs
have bluer dust-corrected UV-r colors on average than the control galaxies by
-0.134 +/- 0.045 magnitudes in FUV-r and -0.075 +/- 0.038 magnitudes in NUV-r,
corresponding to a ~15-20% increase in SSFR. This indicates an enhancement in
SSFR due to tidal interactions. We also find that this relative enhancement is
greater for a subset of r_p < 30 h^-1 kpc pair galaxies, for which the average
colors offsets are -0.193 +/- 0.065 magnitudes in FUV-r and -0.159 +/- 0.048
magnitudes in NUV-r, corresponding to a ~25-30% increase in SSFR. We test for
evolution in the enhancement of tidally-triggered star formation with redshift
across our sample redshift range and find marginal evidence for a decrease in
SSFR enhancement from 0.25 < z < 0.5 to 0.5 < z < 0.75. This indicates that a
change in enhanced star formation triggered by tidal interactions in low
density environments is not a contributor to the decline in the global star
formation rate density across this redshift range.Comment: Accepted for publication in ApJ, emulateapj format, 12 pages, 9
figures, 2 table
Spatial Clustering from GALEX-SDSS samples: Star Formation History and large-scale clustering
We measure the projected spatial correlation function w_p(r_p) from a large
sample combining GALEX ultraviolet imaging with the SDSS spectroscopic sample.
We study the dependence of the clustering strength for samples selected on (NUV
- r)_abs color, specific star formation rate (SSFR), and stellar mass. We find
that there is a smooth transition in the clustering of galaxies as a function
of this color from weak clustering among blue galaxies to stronger clustering
for red galaxies. The clustering of galaxies within the "green valley" has an
intermediate strength, and is consistent with that expected from galaxy groups.
The results are robust to the correction for dust extinction. The comparison
with simple analytical modeling suggests that the halo occupation number
increases with older star formation epochs. When splitting according to SSFR,
we find that the SSFR is a more sensitive tracer of environment than stellar
mass.Comment: Accepted for publication in ApJ; 14 pages, 17 figures, 4 table
Chronique d'une mort annoncée : le destin des galaxies dans un contexte cosmologiques
Sciences de la Terre et de l'Univer