42 research outputs found
On the Luminosity Function of Early--Type Galaxies
In a recent paper Loveday et al. (1992) have presented new results on the
luminosity function for a sample of galaxies with . After having
morphologically classified each galaxy (early--type, late--type, merged or
uncertain), they have estimated the parameters of a Schechter luminosity
function for early-- and late--type galaxies. However, in their sample there is
a bias against identifying early--type galaxies at large distances and/or faint
magnitudes: in fact, many of the early--type galaxies at faint magnitudes have
probably been classified as ``uncertain". As discussed in Loveday et al., the
existence of such a bias is indicated by the fact that for these galaxies
. In this paper we show, both theoretically and through the
use of simulated samples, that this incompleteness strongly biases the derived
parameters of the luminosity function for early--type galaxies. If no
correction for such incompleteness is applied to the data (as done by Loveday
et al.), one obtains a flatter slope and a brighter with respect
to the real parameters.Comment: accepted for publication on MNRAS, Standard TeX, for tables and
figures contact [email protected] BAP 03-1994-04-IR
Probing deviations from General Relativity with the Euclid spectroscopic survey
We discuss the ability of the planned Euclid mission to detect deviations
from General Relativity using its extensive redshift survey of more than 50
Million galaxies. Constraints on the gravity theory are placed measuring the
growth rate of structure within 14 redshift bins between z=0.7 and z=2. The
growth rate is measured from redshift-space distortions, i.e. the anisotropy of
the clustering pattern induced by coherent peculiar motions. This is performed
in the overall context of the Euclid spectroscopic survey, which will
simultaneously measure the expansion history of the universe, using the power
spectrum and its baryonic features as a standard ruler, accounting for the
relative degeneracies of expansion and growth parameters. The resulting
expected errors on the growth rate in the different redshift bins, expressed
through the quantity f\sigma_8, range between 1.3% and 4.4%. We discuss the
optimisation of the survey configuration and investigate the important
dependence on the growth parameterisation and the assumed cosmological model.
We show how a specific parameterisation could actually drive the design towards
artificially restricted regions of the parameter space. Finally, in the
framework of the popular "\gamma -parameterisation", we show that the Euclid
spectroscopic survey alone will already be able to provide substantial evidence
(in Bayesian terms) if the growth index differs from the GR value \gamma=0.55
by at least \sim 0.13. This will combine with the comparable inference power
provided by the Euclid weak lensing survey, resulting in Euclid's unique
ability to provide a decisive test of modified gravity.Comment: 18 pages, 15 figures, accepted by MNRA
The VLA-COSMOS 3 GHz Large Project: Star formation properties and radio luminosity functions of AGN with moderate-to-high radiative luminosities out to
We study a sample of 1,604 moderate-to-high radiative luminosity active
galactic nuclei (HLAGN) selected at 3 GHz within the VLA-COSMOS 3 GHz Large
Project. These were classified by combining multiple AGN diagnostics: X-ray
data, mid-infrared data and broad-band spectral energy distribution fitting. We
decompose the total radio 1.4 GHz luminosity () into
the emission originating from star formation and AGN activity by measuring the
excess in relative to the infrared-radio
correlation of star-forming galaxies. To quantify the excess, for each source
we calculate the AGN fraction (), the fractional contribution
of AGN activity to . The majority of the HLAGN,
, are dominated by star-forming processes (),
while are dominated by AGN-related radio emission
(). We use the AGN-related 1.4 GHz emission to derive the 1.4
GHz AGN luminosity functions of HLAGN. By assuming pure density and pure
luminosity evolution models we constrain their cosmic evolution out to
, finding and . These evolutionary laws show that
the number and luminosity density of HLAGN increased from higher redshifts
() up to a maximum in the redshift range , followed by a
decline towards local values. By scaling the 1.4 GHz AGN luminosity to kinetic
luminosity using the standard conversion, we estimate the kinetic luminosity
density as a function of redshift. We compare our result to the semi-analytic
models of radio mode feedback finding that this feedback could have played an
important role in the context of AGN-host coevolution in HLAGN which show
evidence of AGN-related radio emission ().Comment: 20 pages, 14 figure
Are the Bulk of z > 2 Herschel Galaxies Proto-Spheroids?
We present a backward approach for the interpretation of the evolution of the near-IR and the far-IR luminosity functions (LFs) across the redshift range 0\lt z\lt 3. In our method, late-type galaxies are treated by means of a parametric phenomenological method based on PEP/HerMES data up to z ∼ 4, whereas spheroids are described by means of a physically motivated backward model. The spectral evolution of spheroids is modeled by means of a single-mass model, associated with a present-day elliptical with a K-band luminosity comparable to the break of the local early-type LF. The formation of proto-spheroids is assumed to occurr across the redshift range 1≤slant z≤slant 5. The key parameter is represented by the redshift {{z}0.5} at which half of all proto-spheroids are already formed. For this parameter, a statistical study indicates values between {{z}0.5}=1.5 and {{z}0.5}=3. We assume {{z}0.5}∼ 2 as the fiducial value and show that this assumption allows us to describe accourately the redshift distributions and the source counts. By assuming {{z}0.5}∼ 2 at the far-IR flux limit of the PEP-COSMOS survey, the PEP-selected sources observed at z\gt 2 can be explained as progenitors of local spheroids caught during their formation. We also test the effects of mass downsizing by dividing the spheroids into three populations of different present-day stellar masses. The results obtained in this case confirm the validity of our approach, i.e., that the bulk of proto-spheroids can be modeled by means of a single model that describes the evolution of galaxies at the break of the present-day early-type K-band LF
The web of the Giant: spectroscopic confirmation of a Large Scale Structure around the z=6.31 quasar SDSS J1030+0524
We report on the spectroscopic confirmation of a large scale structure around
the luminous, z=6.31 QSO SDSS~J1030+0524, that is powered by a billion solar
mass black hole. The structure is populated by at least six members, four Lyman
Break Galaxies (LBGs) and two Lyman Alpha Emitters (LAEs). The four LBGs have
been identified among a sample of 21 i-band dropouts with z{AB}<25.5 selected
up to projected separations of 5 physical Mpc (15 arcmin) from the QSO. Their
redshifts have been determined through up to 8hr-long multi-object
spectroscopic observations at 8-10m class telescopes. The two LAEs have been
identified in a 6hr VLT/MUSE observation centered on the QSO. The redshifts of
the six galaxies cover the range 6.129-6.355. Assuming that peculiar velocities
are negligible, this range corresponds to radial separations of +/-5 physical
Mpc from the QSO, that is comparable to the projected scale of the observed LBG
distribution on the sky. We conservatively estimate that this structure is
significant at >3.5 sigma level, and that the level of the galaxy overdensity
is at least 1.5-2 within the large volume sampled (~780 physical Mpc^3). The
spectral properties of the six member galaxies (Lyalpha strength and UV
luminosity) are similar to those of field galaxies at similar redshifts. This
is the first spectroscopic identification of a galaxy overdensity around a
super-massive black hole in the first billion years of the Universe. Our
finding lends support to the idea that the most distant and massive black holes
form and grow within massive (>10^{12} Msun) dark matter halos in large scale
structures, and that the absence of earlier detections of such systems was
likely due to observational limitations.Comment: 8 pages including Appendix, 5 figures, accepted as a letter on
Astronomy & Astrophysics. v2: minor changes in Table 1 caption and Figs. 2 &
3 label
The non-linear infrared-radio correlation of low-z galaxies: implications for redshift evolution, a new radio SFR recipe, and how to minimize selection bias
The infrared-radio correlation (IRRC) underpins many commonly used radio luminosity-star formation rate (SFR) calibrations. In preparation for the new generation of radio surveys we revisit the IRRC of low-z galaxies by (a) drawing on the best currently available IR and 1.4 GHz radio photometry, plus ancillary data over the widest possible area, and (b) carefully assessing potential systematics. We compile a catalogue of ∼9,500 z < 0.2 galaxies and derive their 1.4 GHz radio (L1.4), total IR, and monochromatic IR luminosities in up to seven bands, allowing us to parameterize the wavelength-dependence of monochromatic IRRCs from 22-500 μm. For the first time for low-z samples, we quantify how poorly matched IR and radio survey depths bias measured median IR/radio ratios, q¯¯TIR , and discuss the level of biasing expected for low-z IRRC studies in ASKAP/MeerKAT fields. For our subset of ∼2,000 high-confidence star-forming galaxies we find a median q¯¯TIR of 2.54 (scatter: 0.17 dex). We show that q¯¯TIR correlates with L1.4, implying a non-linear IRRC with slope 1.11±0.01. Our new L1.4-SFR calibration, which incorporates this non-linearity, reproduces SFRs from panchromatic SED fits substantially better than previous IRRC-based recipes. Finally, we match the evolutionary slope of recently measured q¯¯TIR -redshift trends without having to invoke redshift evolution of the IRRC. In this framework, the redshift evolution of q¯¯TIR reported at GHz frequencies in the literature is the consequence of a partial, redshift-dependent sampling of a non-linear IRRC obeyed by low-z and distant galaxies
The SINS/zC-SINF survey of z~2 galaxy kinematics: Outflow properties
Based on SINFONI Ha, [NII] and [SII] AO data of 30 z \sim 2 star-forming
galaxies (SFGs) from the SINS and zcSINF surveys, we find a strong correlation
of the Ha broad flux fraction with the star formation surface density of the
galaxy, with an apparent threshold for strong outflows occurring at 1 Msun
yr^-1 kpc^-2. Above this threshold, we find that SFGs with logm_\ast>10 have
similar or perhaps greater wind mass loading factors (eta = Mdotout/SFR) and
faster outflow velocities than lower mass SFGs. This trend suggests that the
majority of outflowing gas at z \sim 2 may derive from high-mass SFGs, and that
the z \sim 2 mass-metallicity relation is driven more by dilution of enriched
gas in the galaxy gas reservoir than by the efficiency of outflows. The mass
loading factor is also correlated with the SFR and inclination, such that more
star-forming and face-on galaxies launch more powerful outflows. For galaxies
that have evidence for strong outflows, we find that the broad emission is
spatially extended to at least the half-light radius (\sim a few kpc). We
propose that the observed threshold for strong outflows and the observed mass
loading of these winds can be explained by a simple model wherein break-out of
winds is governed by pressure balance in the disk. Using the ratio of the [SII]
doublet in a broad and narrow component, we find that outflowing gas has a
density of \sim10-100 cm^-3, significantly less than that of the star forming
gas (600 cm^-3).Comment: 7 pages, 3 figures, accepted by Ap