39 research outputs found
Testing galaxy formation simulations with damped Lyman-α abundance and metallicity evolution
We examine the properties of damped Lyman- absorbers (DLAs) emerging
from a single set of cosmological initial conditions in two state-of-the-art
cosmological hydrodynamic simulations: {\sc Simba} and {\sc Technicolor Dawn}.
The former includes star formation and black hole feedback treatments that
yield a good match with low-redshift galaxy properties, while the latter uses
multi-frequency radiative transfer to model an inhomogeneous ultraviolet
background (UVB) self-consistently and is calibrated to match the Thomson
scattering optical depth, UVB amplitude, and Ly- forest mean
transmission at . Both simulations are in reasonable agreement with the
measured stellar mass and star formation rate functions at , and both
reproduce the observed neutral hydrogen cosmological mass density, . However, the DLA abundance and metallicity distribution are sensitive
to the galactic outflows' feedback and the UVB amplitude. Adopting a strong UVB
and/or slow outflows under-produces the observed DLA abundance, but yields
broad agreement with the observed DLA metallicity distribution. By contrast,
faster outflows eject metals to larger distances, yielding more metal-rich DLAs
whose observational selection may be more sensitive to dust bias. The DLA
metallicity distribution in models adopting an -regulated star
formation recipe includes a tail extending to , lower than any
DLA observed to date, owing to curtailed star formation in low-metallicity
galaxies. Our results show that DLA observations play an imporant role in
constraining key physical ingredients in galaxy formation models, complementing
traditional ensemble statistics such as the stellar mass and star formation
rate functions.Comment: Accepted for publication in MNRA
2MASS Galaxies in the Fornax Cluster Spectroscopic Survey
The Fornax Cluster Spectroscopic Survey (FCSS) is an all-object survey of a
region around the Fornax Cluster of galaxies undertaken using the 2dF
multi-object spectrograph on the Anglo-Australian Telescope. Its aim was to
obtain spectra for a complete sample of all objects with 16.5 < b_j < 19.7
irrespective of their morphology (i.e. including `stars', `galaxies' and
`merged' images). We explore the extent to which (nearby) cluster galaxies are
present in 2MASS. We consider the reasons for the omission of 2MASS galaxies
from the FCSS and vice versa. We consider the intersection (2.9 square degrees
on the sky) of our data set with the infra-red 2 Micron All-Sky Survey (2MASS),
using both the 2MASS Extended Source Catalogue (XSC) and the Point Source
Catalogue (PSC). We match all the XSC objects to FCSS counterparts by position
and also extract a sample of galaxies, selected by their FCSS redshifts, from
the PSC. We confirm that all 114 XSC objects in the overlap sample are
galaxies, on the basis of their FCSS velocities. A total of 23 Fornax Cluster
galaxies appear in the matched data, while, as expected, the remainder of the
sample lie at redshifts out to z = 0.2 (the spectra show that 61% are early
type galaxies, 18% are intermediate types and 21% are strongly star
forming).The PSC sample turns out to contain twice as many galaxies as does the
XSC. However, only one of these 225 galaxies is a (dwarf) cluster member. On
the other hand, galaxies which are unresolved in the 2MASS data (though almost
all are resolved in the optical) amount to 71% of the non-cluster galaxies with
2MASS detections and have redshifts out to z=0.32.Comment: 5 pages, accepted by A&A, resubmitted due to missing reference
The Optical, Infrared and Radio Properties of Extragalactic Sources Observed by SDSS, 2MASS and FIRST Surveys
We positionally match sources observed by the Sloan Digital Sky Survey
(SDSS), the Two Micron All Sky Survey (2MASS), and the Faint Images of the
Radio Sky at Twenty-cm (FIRST) survey. Practically all 2MASS sources are
matched to an SDSS source within 2 arcsec; ~11% of them are optically resolved
galaxies and the rest are dominated by stars. About 1/3 of FIRST sources are
matched to an SDSS source within 2 arcsec; ~80% of these are galaxies and the
rest are dominated by quasars. Based on these results, we project that by the
completion of these surveys the matched samples will include about 10^7 stars
and 10^6 galaxies observed by both SDSS and 2MASS, and about 250,000 galaxies
and 50,000 quasars observed by both SDSS and FIRST. Here we present a
preliminary analysis of the optical, infrared and radio properties for the
extragalactic sources from the matched samples. In particular, we find that the
fraction of quasars with stellar colors missed by the SDSS spectroscopic survey
is probably not larger than ~10%, and that the optical colors of radio-loud
quasars are ~0.05 mag. redder (with 4-sigma significance) than the colors of
radio-quiet quasars.Comment: 10 pages, 6 color figures, presented at IAU Colloquium 184. AGN
Survey
Galaxy Pairs in the Sloan Digital Sky Survey I: Star Formation, AGN Fraction, and the Luminosity/Mass-Metallicity Relation
(Abridged). We present a sample of 1716 galaxies with companions within Delta
v < 500 km/s, r_p < 80 kpc and stellar mass ratio 0.1 < M_1/M_2 < 10 from the
Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4). In agreement with
previous studies, we find an enhancement in the star formation rate (SFR) of
galaxy pairs at projected separations < 30--40 kpc. In addition, we find that
this enhancement is highest (and extends to the greatest separations) for
galaxies of approximately equal mass, the so-called `major' pairs. However, SFR
enhancement can still be detected for a sample of galaxy pairs whose masses are
within a factor of 10 of each other. In agreement with the one previous study
of the luminosity-metallicity (LZ) relation in paired galaxies, we find an
offset to lower metallicities (by ~ 0.1 dex) for a given luminosity for
galaxies in pairs compared to the control sample. We also present the first
mass-metallicity (MZ) relation comparison between paired galaxies and the
field, and again find an offset to lower metallicities (by ~ 0.05 dex) for a
given mass. The smaller offset in the MZ relation indicates that both higher
luminosities and lower metallicities may contribute to the shift of pairs
relative to the control in the LZ relation. We show that the offset in the LZ
relation depends on galaxy half light radius, r_h. Galaxies with r_h < 3 kpc
and with a close companion show a 0.05-0.1 dex downwards offset in metallicity
compared to control galaxies of the same size. Finally, we study the AGN
fraction in both the pair and control sample and find that whilst selecting
galaxies in different cuts of color and asymmetry yields different AGN
fractions, the fraction for pairs and the control sample are consistent for a
given set of selection criteria.Comment: Accepted for publication in the Astronomical Journa
The evolution of the mass-metallicity relation in SDSS galaxies uncovered by astropaleontology
We have obtained the mass-metallicity (M-Z) relation at different lookback
times for the same set of galaxies from the Sloan Digital Sky Survey, using the
stellar metallicities estimated with our spectral synthesis code STARLIGHT. We
have found that this relation steepens and spans a wider range in both mass and
metallicity at higher redshifts. We have modeled the time evolution of stellar
metallicity with a closed-box chemical evolution model, for galaxies of
different types and masses. Our results suggest that the M-Z relation for
galaxies with present-day stellar masses down to 10^10 M_sun is mainly driven
by the history of star formation history and not by inflows or outflows.Comment: Accepted for publication in MNRA
A 1500 deg2 near infrared proper motion catalogue from the UKIDSS Large Area Survey
The United Kingdom Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) began in 2005, with the start of the UKIDSS programme as a 7 year effort to survey roughly 4000 deg2 at high Galactic latitudes in Y, J, H and K bands. The survey also included a significant quantity of two epoch J band observations, with an epoch baseline greater than 2 years to calculate proper motions. We present a near-infrared proper motion catalogue for the 1500 deg2 of the two epoch LAS data, which includes 135â625 stellar sources and a further 88â324 with ambiguous morphological classifications, all with motions detected above the 5Ï level. We developed a custom proper motion pipeline which we describe here. Our catalogue agrees well with the proper motion data supplied for a 300 deg2 subset in the current Wide Field Camera Science Archive (WSA) 10th data release (DR10) catalogue, and in various optical catalogues, but it benefits from a larger matching radius and hence a larger upper proper motion detection limit. We provide absolute proper motions, using LAS galaxies for the relative to absolute correction. By using local second-order polynomial transformations, as opposed to linear transformations in the WSA, we correct better for any local distortions in the focal plane, not including the radial distortion that is removed by the UKIDSS pipeline. We present the results of proper motion searches for new brown dwarfs and white dwarfs. We discuss 41 sources in the WSA DR10 overlap with our catalogue with proper motions >300âmasâyrâ1, several of which are new detections. We present 15 new candidate ultracool dwarf binary systems
Stellar Populations of Lyman Break Galaxies at z=1-3 in the HST/WFC3 Early Release Science Observations
We analyze the spectral energy distributions (SEDs) of Lyman break galaxies
(LBGs) at z=1-3 selected using the Hubble Space Telescope (HST) Wide Field
Camera 3 (WFC3) UVIS channel filters. These HST/WFC3 observations cover about
50 sq. arcmin in the GOODS-South field as a part of the WFC3 Early Release
Science program. These LBGs at z=1-3 are selected using dropout selection
criteria similar to high redshift LBGs. The deep multi-band photometry in this
field is used to identify best-fit SED models, from which we infer the
following results: (1) the photometric redshift estimate of these dropout
selected LBGs is accurate to within few percent; (2) the UV spectral slope
(beta) is redder than at high redshift (z>3), where LBGs are less dusty; (3) on
average, LBGs at z=1-3 are massive, dustier and more highly star-forming,
compared to LBGs at higher redshifts with similar luminosities
(0.1L*<~L<~2.5L*), though their median values are similar within 1-sigma
uncertainties. This could imply that identical dropout selection technique, at
all redshifts, find physically similar galaxies; and (4) stellar masses of
these LBGs are directly proportional to their UV luminosities with a
logarithmic slope of ~0.46, and star-formation rates are proportional to their
stellar masses with a logarithmic slope of ~0.90. These relations hold true ---
within luminosities probed in this study --- for LBGs from z~1.5 to 5. The
star-forming galaxies selected using other color-based techniques show similar
correlations at z~2, but to avoid any selection biases, and for direct
comparison with LBGs at z>3, a true Lyman break selection at z~2 is essential.
The future HST UV surveys, both wider and deeper, covering a large luminosity
range are important to better understand LBG properties, and their evolution.Comment: Accepted for publication in ApJ (29 pages, 9 figures
Reionization after Planck: the derived growth of the cosmic ionizing emissivity now matches the growth of the galaxy UV luminosity density
Thomson optical depth tau measurements from Planck provide new insights into
the reionization of the universe. In pursuit of model-independent constraints
on the properties of the ionising sources, we determine the empirical evolution
of the cosmic ionizing emissivity. We use a simple two-parameter model to map
out the evolution in the emissivity at z>~6 from the new Planck optical depth
tau measurements, from the constraints provided by quasar absorption spectra
and from the prevalence of Ly-alpha emission in z~7-8 galaxies. We find the
redshift evolution in the emissivity dot{N}_{ion}(z) required by the
observations to be d(log Nion)/dz=-0.15(-0.11)(+0.08), largely independent of
the assumed clumping factor C_{HII} and entirely independent of the nature of
the ionising sources. The trend in dot{N}_{ion}(z) is well-matched by the
evolution of the galaxy UV-luminosity density (dlog_{10}
rho_UV/dz=-0.11+/-0.04) to a magnitude limit >~-13 mag, suggesting that
galaxies are the sources that drive the reionization of the universe. The role
of galaxies is further strengthened by the conversion from the UV luminosity
density rho_UV to dot(N)_{ion}(z) being possible for physically-plausible
values of the escape fraction f_{esc}, the Lyman-continuum photon production
efficiency xi_{ion}, and faint-end cut-off to the luminosity
function. Quasars/AGN appear to match neither the redshift evolution nor
normalization of the ionizing emissivity. Based on the inferred evolution in
the ionizing emissivity, we estimate that the z~10 UV-luminosity density is
8(-4)(+15)x lower than at $z~6, consistent with the observations. The present
approach of contrasting the inferred evolution of the ionizing emissivity with
that of the galaxy UV luminosity density adds to the growing observational
evidence that faint, star-forming galaxies drive the reionization of the
universe.Comment: 20 pages, 12 figures, 5 tables, Astrophysical Journal, updated to
match version in press, Figure 6 shows the main result of the pape
The near-IR properties and continuum shapes of high redshift quasars from the Sloan Digital Sky Survey
We present J-H-K' photometry for a sample of 45 high redshift quasars found
by the Sloan Digital Sky Survey. The sample was originally selected on the
basis of optical colors and spans a redshift range from 3.6 to 5.03. Our
photometry reflects the rest-frame
SED longward of Ly alpha for all redshifts. The results show that the near-IR
colors of high redshift quasars are quite uniform. We have modelled the
continuum shape of the quasars (from just beyond Ly alpha to ~4000 A) with a
power law of the form f_nu \propto nu^alpha, and find =-0.57 with a
scatter of 0.33. This value is similar to what is found for lower redshift
quasars over the same restframe wavelength range, and we conclude that there is
hardly any evolution in the continuum properties of optically selected quasars
up to redshift 5. The spectral indices found by combining near-IR with optical
photometry are in general consistent but slightly flatter than what is found
for the same quasars using the optical spectra and photometry alone, showing
that the continuum region used to determine the spectral indices can somewhat
influence the results.Comment: Accepted for publication in Astronomy and Astrophysic