13 research outputs found
Magellan Spectroscopy of AGN Candidates in the COSMOS Field
We present spectroscopic redshifts for the first 466 X-ray and radio-selected
AGN targets in the 2 deg^2 COSMOS field. Spectra were obtained with the IMACS
instrument on the Magellan (Baade) telescope, using the nod-and-shuffle
technique. We identify a variety of Type 1 and Type 2 AGN, as well as red
galaxies with no emission lines. Our redshift yield is 72% down to i_AB=24,
although the yield is >90% for i_AB<22. We expect the completeness to increase
as the survey continues. When our survey is complete and additional redshifts
from the zCOSMOS project are included, we anticipate ~1100 AGN with redshifts
over the entire COSMOS field. Our redshift survey is consistent with an
obscured AGN population that peaks at z~0.7, although further work is necessary
to disentangle the selection effects.Comment: 19 pages, 14 figures. Accepted to ApJS special COSMOS issue. The full
electronic version of Table 2 can be found at
http://shaihulud.as.arizona.edu/~jtrump/tab2.tx
Optical Identification of the ASCA Large Sky Survey
We present results of optical identification of the X-ray sources detected in
the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34
X-ray sources which were detected with the SIS in the 2-7 keV band above 3.5
sigma. The sources are identified with 30 AGNs, 2 clusters of galaxies, and 1
galactic star. Only 1 source is still unidentified. The flux limit of the
sample corresponds to 1 x 10^{-13} erg s^{-1} cm^{-2} in the 2-10 keV band.
Based on the sample, the paper discusses optical and X-ray spectral
properties of the AGNs, contribution of the sources to the Cosmic X-ray
Background, and redshift and luminosity distributions of the AGNs. An
interesting result is that the redshift distribution of the AGNs suggests a
deficiency of high-redshift (0.5 10^{44}
erg s^{-1}) absorbed narrow-line AGNs (so called type 2 QSOs).Comment: Accepted for publication in ApJ. 57 pages with 13 figures, 9 JPG
plates, 5 additional PS tables. Original EPS plates (gzipped format
~1Mbyte/plate) and TeX tables are available from
ftp://ftp.kusastro.kyoto-u.ac.jp/pub/akiyama/0001289
The XMM-Newton wide-field survey in the COSMOS field: V. Angular Clustering of the X-ray Point Sources
We present the first results of the measurements of angular auto-correlation
functions (ACFs) of X-ray point sources detected in the XMM-Newton observations
of the 2 deg2 COSMOS field (XMM-COSMOS). A significant positive signals have
been detected in the 0.5-2 (SFT) band, in the angle range of 0.5-24 arcminutes,
while the positive signals were at the 2 and 3 sigma levels in the 2-4.5 (MED)
and 4.5-10 (UHD) keV bands respectively. Correctly taking integral constraints
into account is a major limitation in interpreting our results. With power-law
fits to the ACFs without the integral constraint term, we find correlation
lengths of theta_c=1.9+-0.3, 0.8+0.5-0.4 and 6+-2 arcseconds for the SFT, MED,
and UHD bands respectively for gamma=1.8. The inferred comoving correlation
lengths, also taking into account the bias by the source merging due to
XMM-Newton PSF, are 9.8+-0.7, 5.8+1.4-1.7 and 12+-2 h-1 Mpc at the effective
redshifts of 1.1, 0.9, and 0.6 for the SFT, MED, and UHD bands respectively. If
we include the integral constraint term in the fitting process,assuming that
the power-law extends to the scale length of the entire XMM-COSMOSfield, the
correlation lengths become larger by 20%-90%. Comparing the inferred rms
fluctuations of the spatial distribution of AGNs with those of the underlying
mass, the bias parameters of the X-ray source clustering at these effective
redshifts are in the range b(AGN)=1.5-4. (Edited to simple ascii.)Comment: 17 pages, 3 figures Accepted for Astrophysical Journal Supplement
series (COSMOS Special issue
The COSMOS AGN Spectroscopic Survey I: XMM Counterparts
We present optical spectroscopy for an X-ray and optical flux-limited sample
of 677 XMM-Newton selected targets covering the 2 deg^2 COSMOS field, with a
yield of 485 high-confidence redshifts. The majority of the spectra were
obtained over three seasons (2005-2007) with the IMACS instrument on the
Magellan (Baade) telescope. We also include in the sample previously published
Sloan Digital Sky Survey spectra and supplemental observations with
MMT/Hectospec. We detail the observations and classification analyses. The
survey is 90% complete to flux limits of f_{0.5-10 keV}>8 x 10^-16 erg cm^-2
s^-1 and i_AB+<22, where over 90% of targets have high-confidence redshifts.
Making simple corrections for incompleteness due to redshift and spectral type
allows for a description of the complete population to $i_AB+<23. The corrected
sample includes 57% broad emission line (Type 1, unobscured) AGN at
0.13<z<4.26, 25% narrow emission line (Type 2, obscured) AGN at 0.07<z<1.29,
and 18% absorption line (host-dominated, obscured) AGN at 0<z<1.22 (excluding
the stars that made up 4% of the X-ray targets). We show that the survey's
limits in X-ray and optical flux include nearly all X-ray AGN (defined by
L_{0.5-10 keV}>3 x 10^42 erg s^-1) to z<1, of both optically obscured and
unobscured types. We find statistically significant evidence that the obscured
to unobscured AGN ratio at z<1 increases with redshift and decreases with
luminosity.Comment: Accepted for publication in the ApJ. 31 pages, 17 figures. Table 2 is
available on reques
Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
We explore the inter-relationships between mass, star-formation rate and
environment in the SDSS, zCOSMOS and other surveys. The differential effects of
mass and environment are completely separable to z ~ 1, indicating that two
distinct processes are operating, "mass-quenching" and "environment-quenching".
Environment-quenching, at fixed over-density, evidently does not change with
epoch to z ~ 1, suggesting that it occurs as large-scale structure develops in
the Universe. The observed constancy of the mass-function shape for
star-forming galaxies, demands that the mass-quenching of galaxies around and
above M*, must be proportional to their star-formation rates at all z < 2. We
postulate that this simple mass-quenching law also holds over a much broader
range of stellar mass and epoch. These two simple quenching processes, plus
some additional quenching due to merging, then naturally produce (a) a
quasi-static Schechter mass function for star-forming galaxies with a value of
M* that is set by the proportionality between the star-formation and
mass-quenching rates, (b) a double Schechter function for passive galaxies with
two components: the dominant one is produced by mass-quenching and has exactly
the same M* as the star-forming galaxies but an alpha shallower by +1, while
the other is produced by environment effects and has the same M* and alpha as
the star-forming galaxies, and is larger in high density environments.
Subsequent merging of quenched galaxies modifies these predictions somewhat in
the denser environments, slightly increasing M* and making alpha more negative.
All of these detailed quantitative relationships between the Schechter
parameters are indeed seen in the SDSS, lending strong support to our simple
empirically-based model. The model naturally produces for passive galaxies the
"anti-hierarchical" run of mean ages and alpha-element abundances with mass.Comment: 66 pages, 19 figures, 1 movie, accepted for publication in ApJ. The
movie is also available at
http://www.exp-astro.phys.ethz.ch/zCOSMOS/MF_simulation_d1_d4.mo
Exploring the High-redshift PBH-?CDM Universe: Early Black Hole Seeding, the First Stars and Cosmic Radiation Backgrounds
We explore the observational implications of a model in which primordial black holes (PBHs) with a broad birth mass function ranging in mass from a fraction of a solar mass to similar to 10(6) M (circle dot), consistent with current observational limits, constitute the dark matter (DM) component in the universe. The formation and evolution of dark matter and baryonic matter in this PBH-? cold dark matter (?CDM) universe are presented. In this picture, PBH-DM mini-halos collapse earlier than in standard ?CDM, baryons cool to form stars at z similar to 15-20, and growing PBHs at these early epochs start to accrete through Bondi capture. The volume emissivity of these sources peaks at z similar to 20 and rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a channel to make early black hole seeds and naturally account for the origin of an underlying DM halo-host galaxy and central black hole connection that manifests as the M (bh)-sigma correlation. To estimate the luminosity function and contribution to integrated emission power spectrum from these high-redshift PBH-DM halos, we develop a halo occupation distribution model. In addition to tracing the star formation and reionization history, it permits us to evaluate the cosmic infrared and X-ray backgrounds. We find that accretion onto PBHs/active galactic nuclei successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deep IR source count distribution by the James Webb Space Telescope could reveal the existence of this population of high-redshift star-forming and accreting PBH DM
Recommended from our members
Exploring the High-redshift PBH-?CDM Universe: Early Black Hole Seeding, the First Stars and Cosmic Radiation Backgrounds
We explore the observational implications of a model in which primordial black holes (PBHs) with a broad birth mass function ranging in mass from a fraction of a solar mass to similar to 10(6) M (circle dot), consistent with current observational limits, constitute the dark matter (DM) component in the universe. The formation and evolution of dark matter and baryonic matter in this PBH-? cold dark matter (?CDM) universe are presented. In this picture, PBH-DM mini-halos collapse earlier than in standard ?CDM, baryons cool to form stars at z similar to 15-20, and growing PBHs at these early epochs start to accrete through Bondi capture. The volume emissivity of these sources peaks at z similar to 20 and rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a channel to make early black hole seeds and naturally account for the origin of an underlying DM halo-host galaxy and central black hole connection that manifests as the M (bh)-sigma correlation. To estimate the luminosity function and contribution to integrated emission power spectrum from these high-redshift PBH-DM halos, we develop a halo occupation distribution model. In addition to tracing the star formation and reionization history, it permits us to evaluate the cosmic infrared and X-ray backgrounds. We find that accretion onto PBHs/active galactic nuclei successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deep IR source count distribution by the James Webb Space Telescope could reveal the existence of this population of high-redshift star-forming and accreting PBH DM
ROSAT Public PSPC Observations in the Las Campanas Redshift Survey
. The Las Campanas Redshift Survey, an optically selected survey which contains Ăź 26 400 galaxy redshifts, has been correlated with "The First ROSAT Source Catalogue of Pointed Observations with the PSPC," which contains 50 408 sources from 2876 ROSAT pointed observations. Presented here is a description of the optical and x-ray properties of the sample of matched galaxies. 1. The Las Campanas Redshift Survey (LCRS) The Las Campanas Redshift Survey (LCRS; Shectman et al. 1995) is an optically selected galaxy redshift survey which extends to a redshift of 0.2 and which is composed of a total of 6 alternating 1: ffi 5 \Theta 80 ffi slices in the North and South Galactic Caps. Accurate R-band photometry and sky positions for program objects have been extracted from CCD drift scans obtained on the Las Campanas Swope 1-m telescope; spectroscopy has been performed at the Las Campanas Du Pont 2.5-m telescope, originally via a 50-fiber Multi-Object Spectrograph (MOS), and later via a 112-..