140 research outputs found
Simultaneous Estimation of Photometric Redshifts and SED Parameters: Improved Techniques and a Realistic Error Budget
We seek to improve the accuracy of joint galaxy photometric redshift
estimation and spectral energy distribution (SED) fitting. By simulating
different sources of uncorrected systematic errors, we demonstrate that if the
uncertainties on the photometric redshifts are estimated correctly, so are
those on the other SED fitting parameters, such as stellar mass, stellar age,
and dust reddening. Furthermore, we find that if the redshift uncertainties are
over(under)-estimated, the uncertainties in SED parameters tend to be
over(under)-estimated by similar amounts. These results hold even in the
presence of severe systematics and provide, for the first time, a mechanism to
validate the uncertainties on these parameters via comparison with
spectroscopic redshifts. We propose a new technique (annealing) to re-calibrate
the joint uncertainties in the photo-z and SED fitting parameters without
compromising the performance of the SED fitting + photo-z estimation. This
procedure provides a consistent estimation of the multidimensional probability
distribution function in SED fitting + z parameter space, including all
correlations. While the performance of joint SED fitting and photo-z estimation
might be hindered by template incompleteness, we demonstrate that the latter is
"flagged" by a large fraction of outliers in redshift, and that significant
improvements can be achieved by using flexible stellar populations synthesis
models and more realistic star formation histories. In all cases, we find that
the median stellar age is better recovered than the time elapsed from the onset
of star formation [abridged].Comment: 11 pages, 5 figures, 3 tables. Accepted for publication in the
Astrophysical Journa
The RedGOLD cluster detection algorithm and its cluster candidate catalogue for the CFHT-LS W1
We present RedGOLD (Red-sequence Galaxy Overdensity cLuster Detector), a new optical/NIR galaxy cluster detection algorithm, and apply it to the CFHT-LS W1 field. RedGOLD searches for red-sequence galaxy overdensities while minimizing contamination from dusty star-forming galaxies. It imposes an Navarro–Frenk–White profile and calculates cluster detection significance and richness. We optimize these latter two parameters using both simulations and X-ray-detected cluster catalogues, and obtain a catalogue ∼80 per cent pure up to z ∼ 1, and ∼100 per cent (∼70 per cent) complete at z ≤ 0.6 (z ≲ 1) for galaxy clusters with M ≳ 10^(14) M_⊙ at the CFHT-LS Wide depth. In the CFHT-LS W1, we detect 11 cluster candidates per deg^2 out to z ∼ 1.1. When we optimize both completeness and purity, RedGOLD obtains a cluster catalogue with higher completeness and purity than other public catalogues, obtained using CFHT-LS W1 observations, for M ≳ 10^(14) M_⊙. We use X-ray-detected cluster samples to extend the study of the X-ray temperature–optical richness relation to a lower mass threshold, and find a mass scatter at fixed richness of σ_(lnM|λ) = 0.39 ± 0.07 and σ_(lnM|λ) = 0.30 ± 0.13 for the Gozaliasl et al. and Mehrtens et al. samples. When considering similar mass ranges as previous work, we recover a smaller scatter in mass at fixed richness. We recover 93 per cent of the redMaPPer detections, and find that its richness estimates is on average ∼40–50 per cent larger than ours at z > 0.3. RedGOLD recovers X-ray cluster spectroscopic redshifts at better than 5 per cent up to z ∼ 1, and the centres within a few tens of arcseconds
Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe
We compare state-of-the-art semi-analytic models of galaxy formation as well
as advanced sub-halo abundance matching models with a large sample of
early-type galaxies from SDSS at z < 0.3. We focus our attention on the
dependence of median sizes of central galaxies on host halo mass. The data do
not show any difference in the structural properties of early-type galaxies
with environment, at fixed stellar mass. All hierarchical models considered in
this work instead tend to predict a moderate to strong environmental
dependence, with the median size increasing by a factor of about 1.5-3 when
moving from low to high mass host haloes. At face value the discrepancy with
the data is highly significant, especially at the cluster scale, for haloes
above log Mhalo > 14. The convolution with (correlated) observational errors
reduces some of the tension. Despite the observational uncertainties, the data
tend to disfavour hierarchical models characterized by a relevant contribution
of disc instabilities to the formation of spheroids, strong gas dissipation in
(major) mergers, short dynamical friction timescales, and very short quenching
timescales in infalling satellites. We also discuss a variety of additional
related issues, such as the slope and scatter in the local size-stellar mass
relation, the fraction of gas in local early-type galaxies, and the general
predictions on satellite galaxies.Comment: 27 pages, 14 figures, 2 tables. MNRAS, in pres
Spectroscopic Confirmation of the Rich z=1.80 Galaxy Cluster JKCS 041 Using the WFC3 Grism: Environmental Trends in the Ages and Structure of Quiescent Galaxies
We present Hubble Space Telescope imaging and grism spectroscopy of the distant galaxy cluster JKCS041. Our survey yields 98 redshifts whose precision is typically ~20 times better than photometric estimates. We confirm that JKCS041 is a rich cluster and derive a redshift z=1.80 via the identification of 19 member galaxies, of which 15 are quiescent. These members are spatially aligned with diffuse X-ray emission seen by Chandra. As JKCS041 is the most distant known cluster with such a large and spectroscopically-confirmed quiescent population, it provides an unique opportunity to study the effect of the environment on galaxy properties at early epochs. We construct composite spectra of the quiescent members that clearly reveal Balmer and metallic absorption lines. From these, we infer that the more massive members (M_*>10^(11)M_☉) have a mean stellar age of 1.4^(+0.3)_(-0.2) Gyr, whereas lower-mass examples (M_*=10^(10.5-11)M_☉) have a younger mean age of 0.9^(+0.2)_(-0.1) Gyr. These ages agree closely with those inferred by Whitaker et al. for similarly-selected quiescent field galaxies, supporting the idea that the cluster environment is more efficient at truncating star formation while not having a strong effect on the mean epoch of quenching. In contrast to field samples, there is no sign of low-level Hβ or [O III] emission in our composite spectra. By comparing the ellipticity distribution of the quiescent members to coeval field galaxies drawn from the CANDELS survey, we find some evidence (90% confidence) for a lower fraction of disk-like quiescent systems in JKCS041. Taking this into account, we do not detect a significant difference between the mass-radius relations of the quiescent JKCS041 members and our z~1.8 field sample. We review claims of environmentally-dependent size growth of z>1 quiescent galaxies, and we demonstrate how differences in morphological mixtures may complicate comparisons of sizes in different environments
NEAR-ULTRAVIOLET SPECTROSCOPY of STAR-FORMING GALAXIES from eBOSS: SIGNATURES of UBIQUITOUS GALACTIC-SCALE OUTFLOWS
The Astrophysical Journal 815.1 (2015): 48 reproduced by permission of the AASWe present rest-frame near-ultraviolet (NUV) spectroscopy of star-forming galaxies (SFGs) at 0.6 < z < 1.2 from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) in SDSS-IV. One of the eBOSS programs is to obtain 2″ (about 15 kpc) fiber spectra of about 200,000 emission-line galaxies (ELGs) at redshift z ≥ 0.6. We use the data from the pilot observations of this program, including 8620 spectra of SFGs at 0.6 < z < 1.2. The median composite spectra of these SFGs at 2200 A < λ < 4000 A feature asymmetric, preferentially blueshifted non-resonant emission, Fe ii∗, and blueshifted resonant absorption, e.g., Fe ii and Mg ii, indicating ubiquitous outflows driven by star formation at these redshifts. For the absorption lines, we find a variety of velocity profiles with different degrees of blueshift. Comparing our new observations with the literature, we do not observe the non-resonant emission in the small-aperture (<40 pc) spectra of local star-forming regions with the Hubble Space Telescope, and find the observed line ratios in the SFG spectra to be different from those in the spectra of local star-forming regions, as well as those of quasar absorption-line systems in the same redshift range. We introduce an outflow model that can simultaneously explain the multiple observed properties and suggest that the variety of absorption velocity profiles and the line ratio differences are caused by scattered fluorescent emission filling in on top of the absorption in the large-aperture eBOSS spectra. We develop an observation-driven, model-independent method to correct the emission infill to reveal the true absorption profiles. Finally, we show that the strengths of both the non-resonant emission and the emission-corrected resonant absorption increase with [O ii] λλ3727, 3730 rest equivalent width and luminosity, with a slightly larger dependence on the former. Our results show that the eBOSS and future dark-energy surveys (e.g., Dark Energy Spectroscopic Instrument survey and Prime Focus Spectrograph survey) will provide rich data sets of rest-frame NUV spectroscopy for astrophysical applicationsG.B.Z. started this work when he was visiting Princeton University in 2014 December and he would like to thank Michael Strauss and Jim Gunn for their hospitality. He also thanks Bruce Draine, Tim Heckman, Claus Leitherer, Jason X. Prochaska, and Rosie Wise for useful discussions. G.B.Z. acknowledges support provided by NASA through Hubble Fellowship grant #HST-HF2-51351 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract NAS 5-26555. We thank an anonymous referee for helpful comments that have helped improve the paper.
J.C. acknowledges financial support from MINECO (Spain) under project number AYA2012-31101. J.-P.K. and T.D. acknowledge support from the LIDA ERC advanced grant. A.R. acknowledges funding from the P2IO LabEx (ANR-10-LABX-0038) in the framework “Investissements d’Avenir” (ANR-11-IDEX-0003-01) managed by the French National Research Agency (ANR
Avoiding Progenitor Bias: The Structural and Mass Evolution of Brightest Group and Cluster Galaxies in Hierarchical Models since z≾1
The mass and structural evolution of massive galaxies is one of the hottest topics in galaxy formation. This is because it may reveal invaluable insights into the still debated evolutionary processes governing the growth and assembly of spheroids. However, direct comparison between models and observations is usually prevented by the so-called progenitor bias, i.e., new galaxies entering the observational selection at later epochs, thus eluding a precise study of how pre-existing galaxies actually evolve in size. To limit this effect, we here gather data on high-redshift brightest group and cluster galaxies, evolve their (mean) host halo masses down to z = 0 along their main progenitors, and assign as their "descendants" local Sloan Digital Sky Survey central galaxies matched in host halo mass. At face value, the comparison between high redshift and local data suggests a noticeable increase in stellar mass of a factor of ≳ 2 since z ~ 1, and of ≳ 2.5 in mean effective radius. We then compare the inferred stellar mass and size growth with those predicted by hierarchical models for central galaxies, selected at high redshifts to closely match the halo and stellar mass bins as in the data. Only hierarchical models characterized by very limited satellite stellar stripping and parabolic orbits are capable of broadly reproducing the stellar mass and size increase of a factor of ~2-4 observed in cluster galaxies since z ~ 1. The predicted, average (major) merger rate since z ~ 1 is in good agreement with the latest observational estimates
The Next Generation Virgo Cluster Survey. XX. RedGOLD Background Galaxy Cluster Detections
We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey (NGVS) using our detection algorithm RedGOLD. The NGVS covers 104 deg^2 of the Virgo cluster in the u*, g, r, i, z-bandpasses to a depth of g ~ 25.7 mag (5σ). Part of the survey was not covered or has shallow observations in the r band. We build two cluster catalogs: one using all bandpasses, for the fields with deep r-band observations (~20 deg^2), and the other using four bandpasses (u*, g, i, z) for the entire NGVS area. Based on our previous Canada–France–Hawaii Telescope Legacy Survey W1 studies, we estimate that both of our catalogs are ~100% (~70%) complete and ~80% pure, at z ≤ 0.6 (z ≾1), for galaxy clusters with masses of M ≳ 10^(14) M⊙. We show that when using four bandpasses, though the photometric redshift accuracy is lower, RedGOLD detects massive galaxy clusters up to z ~ 1 with completeness and purity similar to the five-band case. This is achieved when taking into account the bias in the richness estimation, which is ~40% lower at 0.5 ≤ z 1.4 × 10^(14) M⊙ and 0.08 < z < 0.5. Because of our different cluster richness limits and the NGVS depth, our catalogs reach lower masses than the published redMaPPer cluster catalog over the area, and we recover ~90%–100% of its detections
The Next Generation Virgo Cluster Survey - Infrared (NGVS-IR): I. A new Near-UV/Optical/Near-IR Globular Cluster selection tool
The NGVS-IR project (Next Generation Virgo Survey - Infrared) is a contiguous
near-infrared imaging survey of the Virgo cluster of galaxies. It complements
the optical wide-field survey of Virgo (NGVS). The current state of NGVS-IR
consists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-band
imaging of 16 deg^2 covering the region between M49 and M87. In this paper, we
present the observations of the central 4 deg^2 centered on Virgo's core
region. The data were acquired with WIRCam on the Canada-France-Hawaii
Telescope and the total integration time was 41 hours distributed in 34
contiguous tiles. A survey-specific strategy was designed to account for
extended galaxies while still measuring accurate sky brightness within the
survey area. The average 5\sigma limiting magnitude is Ks=24.4 AB mag and the
50% completeness limit is Ks=23.75 AB mag for point source detections, when
using only images with better than 0.7" seeing (median seeing 0.54"). Star
clusters are marginally resolved in these image stacks, and Virgo galaxies with
\mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with optical
and ultraviolet data, we build the uiK color-color diagram which allows a very
clean color-based selection of globular clusters in Virgo. This diagnostic plot
will provide reliable globular cluster candidates for spectroscopic follow-up
campaigns needed to continue the exploration of Virgo's photometric and
kinematic sub-structures, and will help the design of future searches for
globular clusters in extragalactic systems. Equipped with this powerful new
tool, future NGVS-IR investigations based on the uiK diagram will address the
mapping and analysis of extended structures and compact stellar systems in and
around Virgo galaxies.Comment: 23 pages, 18 figures. Accepted for publication in ApJ
Evolution of Star-forming Galaxies from z=0.7 to 1.2 with eBOSS Emission-line Galaxies
We study the evolution of star-forming galaxies with 10 10 M ⊙ < M ∗ < 10 11.6 M ⊙ over the redshift range of 0.7 < z < 1.2 using the emission-line galaxies (ELGs) in the extended Baryon Oscillation Spectroscopic Survey (eBOSS). By applying the incomplete conditional stellar mass function (SMF) model proposed in Guo et al., we simultaneously constrain the sample completeness, the stellariVhalo mass relation (SHMR), and the quenched galaxy fraction. We obtain the intrinsic SMFs for star-forming galaxies in the redshift bins of 0.7 < z < 0.8, 0.8 < z < 0.9, 0.9 < z < 1.0, and 1.0 < z < 1.2, as well as the SMF for all galaxies in the redshift bin of 0.7 < z < 0.8. We find that the eBOSS ELG sample only selects about 1%-10% of the star-forming galaxy population at the different redshifts, with the lower redshift samples more complete. There is only weak evolution in the SHMR of the ELGs from z = 1.2 to z = 0.7, as well as the intrinsic galaxy SMFs. Our best-fitting models show that the central ELGs at these redshifts live in halos of mass M ∼ 10 12 M ⊙ , while the satellite ELGs occupy slightly more massive halos of M ∼ 10 12.6 M ⊙ . The average satellite fraction of the observed ELGs varies from 13% to 17%, with the galaxy bias increasing from 1.1 to 1.4 from z = 0.7 to 1.2
Early-type galaxies at z = 1.3. I. The Lynx supercluster: cluster and groups at z=1.3. Morphology and color-magnitude relation
We confirm the detection of 3 groups in the Lynx supercluster, at z~1.3, and
give their redshifts and masses. We study the properties of the group galaxies
as compared to the central clusters, RXJ0849+4452 and RXJ0848+4453, selecting
89 galaxies in the clusters and 74 galaxies in the groups. We morphologically
classify galaxies by visual inspection, noting that our early-type galaxy (ETG)
sample would have been contaminated at the 30% -40% level by simple automated
classification methods (e.g. based on Sersic index). In luminosity selected
samples, both clusters and groups show high fractions of Sa galaxies. The ETG
fractions never rise above ~50% in the clusters, which is low compared to the
fractions observed in clusters at z~1. However, ETG plus Sa fractions are
similar to those observed for ETGs in clusters at z~1. Bulge-dominated galaxies
visually classified as Sas might also be ETGs with tidal features or merger
remnants. They are mainly red and passive, and span a large range in
luminosity. Their star formation seems to have been quenched before
experiencing a morphological transformation. Because their fraction is smaller
at lower redshifts, they might be the spiral population that evolves into ETGs.
For mass-selected samples, the ETG fraction show no significant evolution with
respect to local clusters, suggesting that morphological transformations occur
at lower masses and densities. The ETG mass-size relation shows evolution
towards smaller sizes at higher redshift in both clusters and groups, while the
late-type mass-size relation matches that observed locally. The group ETG red
sequence shows lower zero points and larger scatters than in clusters, both
expected to be an indication of a younger galaxy population. The estimated age
difference is small when compared to the difference in age at different galaxy
masses.Comment: ApJ, submitted - referee report answered - iterating with the refere
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