ABSTRACT We use Hubble Space Telescope/WFC3 imaging to study the red population in the IR-selected, X-ray detected, low-mass cluster Cl J1449+0856 at z = 2, one of the few bona fide established ...clusters discovered at this redshift, and likely a typical progenitor of an average massive cluster today. This study explores the presence and significance of an early red sequence in the core of this structure, investigating the nature of red-sequence galaxies, highlighting environmental effects on cluster galaxy populations at high redshift, and at the same time underlining similarities and differences with other distant dense environments. Our results suggest that the red population in the core of Cl J1449+0856 is made of a mixture of quiescent and dusty star-forming galaxies, with a seedling of the future red sequence already growing in the very central cluster region, and already characterizing the inner cluster core with respect to lower-density environments. On the other hand, the color-magnitude diagram of this cluster is definitely different from that of lower-redshift z 1 clusters, as well as of some rare particularly evolved massive clusters at similar redshift, and it is suggestive of a transition phase between active star formation and passive evolution occurring in the protocluster and established lower-redshift cluster regimes.
ABSTRACT
We use a background quasar to detect the presence of circumgalactic gas around a
low-mass star-forming galaxy. Data from the new Multi Unit Spectroscopic Explorer (MUSE) on the Very Large ...Telescope show that the galaxy has a dust-corrected star formation rate (SFR) of 4.7 ± 2.0
M
⊙
yr
−1
, with no companion down to 0.22
M
⊙
yr
−1
(5
σ
) within 240
kpc (“30”). Using a high-resolution spectrum of the background quasar, which is fortuitously aligned with the galaxy major axis (with an azimuth angle
α
of only 15°), we find, in the gas kinematics traced by low-ionization lines, distinct signatures consistent with those expected for a “cold-flow disk” extending at least 12 kpc (
). We estimate the mass accretion rate
to be at least two to three times larger than the SFR, using the geometric constraints from the IFU data and the H
i
column density of log
/
≃ 20.4 obtained from a
Hubble Space Telescope
/COS near-UV spectrum. From a detailed analysis of the low-ionization lines (e.g., Zn
ii
, Cr
ii
, Ti
ii
, Mn
ii
, Si
ii
), the accreting material appears to be enriched to about 0.4
(albeit with large uncertainties:
), which is comparable to the galaxy metallicity (12 + log O/H = 8.7 ± 0.2), implying a large recycling fraction from past outflows. Blueshifted Mg
ii
and Fe
ii
absorptions in the galaxy spectrum from the MUSE data reveal the presence of an outflow. The Mg
ii
and Fe
ii
absorption line ratios indicate emission infilling due to scattering processes, but the MUSE data do not show any signs of fluorescent Fe
ii
* emission.
HDUV: The Hubble Deep UV Legacy Survey Oesch, P. A.; Montes, M.; Reddy, N. ...
The Astrophysical journal. Supplement series,
07/2018, Letnik:
237, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We present the Hubble Deep UV Legacy Survey (HDUV), a 132-orbit imaging program with the WFC3/UVIS camera on board the
Hubble Space Telescope
(
HST
). The HDUV extends and builds on the few ...previous UV imaging surveys in the two GOODS/CANDELS-Deep fields to provide deep images over a total area of ∼100 arcmin
2
in the two filters F275W and F336W. Our release also includes all the F275W imaging data taken by the CANDELS survey, which were aligned using a novel approach and combined with the HDUV survey data. By reaching depths of 27.5–28.0 mag (5
σ
in 0.″4 apertures), these are the deepest high-resolution UV data over such a large area taken to date. Such unique UV imaging enables a wide range of science by the community. A few of the main goals of the HDUV survey are as follows: (1) to provide a complete sample of faint star-forming galaxies at
z
∼ 1–3; (2) to constrain the ionizing photon escape fraction from galaxies at
z
∼ 2–3; and (3) to track the build-up of bulges and the disappearance of clumpy disk galaxies through reliable internal stellar population properties at sub-kiloparsec resolution out to
z
∼ 3. The addition of the HDUV data further enhances the legacy value of the two GOODS/CANDELS-Deep fields, which now include deep 11-band
HST
imaging, as well as very deep ancillary data from X-ray to radio, enabling unique multi-wavelength studies. Here, we provide an overview of the survey design, describe the data reduction, and highlight a few basic analyses of the images that are available to the community as high-level science products, via the Mikulski Archive for Space Telescopes.
The HUDF09 data are the deepest near-IR observations ever, reaching to 29.5 mag. Luminosity functions (Lfs) from these new HUDF09 data for 132 z ~ 7 and z ~ 8 galaxies are combined with new LFs for z ...~ 5-6 galaxies and the earlier z ~ 4 LF to reach to very faint limits. The faint-end slopes alpha are steep: -1.79 + or - 0.12, -1.73 + or - 0.20, -2.01 + or - 0.21, and -1.91 + or - 0.32. Slopes alpha -2 lead to formally divergent UV fluxes, though galaxies are not expected to form below ~-10 AB mag. It may thus not be necessary to resort to extreme assumptions about the escape fraction or clumping factor. Nevertheless, the uncertainties remain large. Deeper WFC3/IR+ACS observations can further constrain the UV ionizing flux from faint galaxies.
We perform a search for stellar streams around the Milky Way using the first 3 yr of multiband optical imaging data from the Dark Energy Survey (DES). We use DES data covering ∼5000 deg2 to a depth ...of g > 23.5 with a relative photometric calibration uncertainty of <1%. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of ∼50 kpc. We search for stellar streams using a matched filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of 11 new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extratidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, and the large- and small-scale distribution of dark matter around the Milky Way.
THE zCOSMOS 20k GROUP CATALOG KNOBEL, C; LILLY, S. J; KNEIB, J.-P ...
The Astrophysical journal,
07/2012, Letnik:
753, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We present an optical group catalog between 0.1 <, ~ z <, ~ 1 based on 16,500 high-quality spectroscopic redshifts in the completed zCOSMOS-bright survey. The catalog published herein contains 1498 ...groups in total and 192 groups with more than five observed members. The catalog includes both group properties and the identification of the member galaxies. Based on mock catalogs, the completeness and purity of groups with three and more members should be both about 83% with respect to all groups that should have been detectable within the survey, and more than 75% of the groups should exhibit a one-to-one correspondence to the "real" groups. Particularly at high redshift, there are apparently more galaxies in groups in the COSMOS field than expected from mock catalogs. We detect clear evidence for the growth of cosmic structure over the last seven billion years in the sense that the fraction of galaxies that are found in groups (in volume-limited samples) increases significantly with cosmic time. In the second part of the paper, we develop a method for associating galaxies that only have photo-z to our spectroscopically identified groups. We show that this leads to improved definition of group centers, improved identification of the most massive galaxies in the groups, and improved identification of central and satellite galaxies, where we define the former to be galaxies at the minimum of the gravitational potential wells. Subsamples of centrals and satellites in the groups can be defined with purities up to 80%, while a straight binary classification of all group and non-group galaxies into centrals and satellites achieves purities of 85% and 75%, respectively, for the spectroscopic sample.
In this paper, we present an exact general analytic expression
$Z({\rm sSFR})={y_Z \over \Lambda ({\rm sSFR})}+I({\rm sSFR})$
linking the gas metallicity Z to the specific star formation rate (sSFR), ...which validates and extends the approximate relation put forward by Lilly et al. (L13), where y
z
is the yield per stellar generation, Λ(sSFR) is the instantaneous ratio between inflow and star formation rate expressed as a function of the sSFR and I is the integral of the past enrichment history, respectively. We then demonstrate that the instantaneous metallicity of a self-regulating system, such that its sSFR decreases with decreasing redshift, can be well approximated by the first term on the right-hand side in the above formula, which provides an upper bound to the metallicity. The metallicity is well approximated also by
$Z_{{{\rm L13}}}^{{\rm id}}=Z({\rm sSFR})={y_Z \over 1+\eta +{\rm sSFR}/\nu}$
(L13 ideal regulator case), which provides a lower bound to the actual metallicity. We compare these approximate analytic formulae to numerical results and infer a discrepancy <0.1 dex in a range of metallicities (
${\rm log} (Z\mathrm{/Z}_{{\odot }})\in {-}1.5,0$
, for y
z
≡ Z⊙ = 0.02) and almost three orders of magnitude in the sSFR. We explore the consequences of the L13 model on the mass-weighted metallicity in the stellar component of the galaxies. We find that the stellar average metallicity lags ∼0.1–0.2 dex behind the gas-phase–metallicity relation, in agreement with the data.
We search for z ~ 10 galaxies over ~160 arcmin super(2) of Wide-Field Camera 3 (WFC3)/IR data in the Chandra Deep Field South, using the public HUDF09, Early Release Science, and CANDELS surveys, ...that reach to 5sigma depths ranging from 26.9 to 29.4 in H sub(160) AB mag. z > ~ 9.5 galaxy candidates are identified via J sub(125) - H sub(160) > 1.2 colors and non-detections in any band blueward of J sub(125). Spitzer Infrared Array Camera (IRAC) photometry is key for separating the genuine high-z candidates from intermediate-redshift (z ~ 2-4) galaxies with evolved or heavily dust obscured stellar populations. After removing 16 sources of intermediate brightness (H sub(160) ~ 24-26 mag) with strong IRAC detections, we only find one plausible z ~ 10 galaxy candidate in the whole data set, previously reported in Bouwens et al.. The newer data cover a 3 x larger area and provide much stronger constraints on the evolution of the UV luminosity function (LF). If the evolution of the z ~ 4-8 LFs is extrapolated to z ~ 10, six z ~ 10 galaxies are expected in our data. The detection of only one source suggests that the UV LF evolves at an accelerated rate before z ~ 8. The luminosity density is found to increase by more than an order of magnitude in only 170 Myr from z ~ 10 to z ~ 8. This increase is > or =4 x larger than expected from the lower redshift extrapolation of the UV LF. We are thus likely witnessing the first rapid buildup of galaxies in the heart of cosmic reionization. Future deep Hubble Space Telescope WFC3/IR data, reaching to well beyond 29 mag, can enable a more robust quantification of the accelerated evolution around z ~ 10.
In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a ...large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg2 of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Delta *Dz > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H AB = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band.
We have studied the properties of giant star-forming clumps in five z {approx} 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the ...Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H{alpha}/N II line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km s{sup -1} kpc{sup -1}, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.
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