557 research outputs found
Obscuration by Gas and Dust in Luminous Quasars
We explore the connection between absorption by neutral gas and extinction by
dust in mid-infrared (IR) selected luminous quasars. We use a sample of 33
quasars at redshifts 0.7 < z < 3 in the 9 deg^2 Bo\"otes multiwavelength survey
field that are selected using Spitzer Space Telescope Infrared Array Camera
colors and are well-detected as luminous X-ray sources (with >150 counts) in
Chandra observations. We divide the quasars into dust-obscured and unobscured
samples based on their optical to mid-IR color, and measure the neutral
hydrogen column density N_H through fitting of the X-ray spectra. We find that
all subsets of quasars have consistent power law photon indices equal to 1.9
that are uncorrelated with N_H. We classify the quasars as gas-absorbed or
gas-unabsorbed if N_H > 10^22 cm^-2 or N_H < 10^22 cm^-2, respectively. Of 24
dust-unobscured quasars in the sample, only one shows clear evidence for
significant intrinsic N_H, while 22 have column densities consistent with N_H <
10^22 cm^-2. In contrast, of the nine dust-obscured quasars, six show evidence
for intrinsic gas absorption, and three are consistent with N_H < 10^22 cm^-2.
We conclude that dust extinction in IR-selected quasars is strongly correlated
with significant gas absorption as determined through X-ray spectral fitting.
These results suggest that obscuring gas and dust in quasars are generally
co-spatial, and confirm the reliability of simple mid-IR and optical
photometric techniques for separating quasars based on obscuration.Comment: 5 pages, 3 figure
First Weak-lensing Results from "See Change": Quantifying Dark Matter in the Two Z>1.5 High-redshift Galaxy Clusters SPT-CL J2040-4451 and IDCS J1426+3508
We present a weak-lensing study of SPT-CLJ2040-4451 and IDCSJ1426+3508 at
z=1.48 and 1.75, respectively. The two clusters were observed in our "See
Change" program, a HST survey of 12 massive high-redshift clusters aimed at
high-z supernova measurements and weak-lensing estimation of accurate cluster
masses. We detect weak but significant galaxy shape distortions using IR images
from the WFC3, which has not yet been used for weak-lensing studies. Both
clusters appear to possess relaxed morphology in projected mass distribution,
and their mass centroids agree nicely with those defined by both the galaxy
luminosity and X-ray emission. Using an NFW profile, for which we assume that
the mass is tightly correlated with the concentration parameter, we determine
the masses of SPT-CL J2040-4451 and IDCS J1426+3508 to be
M_{200}=8.6_{-1.4}^{+1.7}x10^14 M_sun and 2.2_{-0.7}^{+1.1}x10^14 M_sun,
respectively. The weak-lensing mass of SPT-CLJ2040-4451 shows that the cluster
is clearly a rare object. Adopting the central value, the expected abundance of
such a massive cluster at z>1.48 is only ~0.07 in the parent 2500 sq. deg.
survey. However, it is yet premature to claim that the presence of this cluster
creates a serious tension with the current LCDM paradigm unless that tension
will remain in future studies after marginalizing over many sources of
uncertainties such as the accuracy of the mass function and the
mass-concentration relation at the high mass end. The mass of IDCSJ1426+3508 is
in excellent agreement with our previous ACS-based weak-lensing result while
the much higher source density from our WFC3 imaging data makes the current
statistical uncertainty ~40% smaller.Comment: Accepted to Ap
The Subillimeter Properties of Extremely Red Objects in the CUDSS Fields
We discuss the submillimeter properties of Extremely Red Objects (EROs) in
the two Canada-UK Deep Submillimeter Survey (CUDSS) Fields. We measure the mean
submillimeter flux of the ERO population (to K < 20.7) and find 0.4 +/- 0.07
mJy for EROs selected by (I-K) > 4.0 and 0.56 +/- 0.09 mJy for EROs selected by
(R-K) > 5.3 but, these measurements are dominated by discrete, bright
submillimeter sources. We estimate that EROs produce 7-11% of the far-infrared
background at 850um. This is substantially less than a previous measurement by
Wehner, Barger & Kneib (2002) and we discuss possible reasons for this
discrepancy. We show that ERO counterparts to bright submillimeter sources lie
within the starburst region of the near-infrared color-color plot of Pozzetti &
Mannucci (2000). Finally, we claim that pairs or small groups of EROs with
separations of < 10 arcseconds often mark regions of strong submillimeter flux.Comment: 9 pages, 8 figures, accepted for publication in Ap
Near-Infrared Spectroscopy of 0.4<z<1.0 CFRS Galaxies: Oxygen Abundances, SFRs and Dust
Using new J-band VLT-ISAAC and Keck-NIRSPEC spectroscopy, we have measured
Halpha and [NII] line fluxes for 0.47<z<0.92 CFRS galaxies which have [OII],
Hbeta and [OIII]a line fluxes available from optical spectroscopy, to
investigate how the properties of the star forming gas in galaxies evolve with
redshift. We derive the extinction and oxygen abundances for the sample using a
method based on a set of ionisation parameter and oxygen abundance diagnostics,
simultaneously fitting the [OII], Hbeta,[OIII], Halpha, and [NII] line fluxes.
The individual reddening measurements allow us to accurately correct the
Halpha-based star formation rate (SFR) estimates for extinction. Our most
salient conclusions are: a) in all 30 CFRS galaxies the source of gas
ionisation is not due to AGN activity; b) we find a range of 0<AV<3, suggesting
that it is important to determine the extinction for every single galaxy in
order to reliably measure SFRs and oxygen abundances in high redshift galaxies;
c) high values of [NII]/Halpha >0.1 for most (but not all) of the CFRS galaxies
indicate that they lie on the high-metallicity branch of the R23 calibration;
d) about one third of the 0.47<z<0.92 CFRS galaxies in our sample have lower
metallicities than local galaxies with similar luminosities and star formation
rates; e) comparison with a chemical evolution model indicates that these low
metallicity galaxies are unlikely to be the progenitors of metal-poor dwarf
galaxies at z~0.Comment: Accepted for publication in the Astrophysical Journa
Attitudes toward people with disabilities in the social context of dating and marriage: A comparison of American, Taiwanese, and Singaporean college students
The purpose of this study is to examine the attitudes of American, Taiwanese, and Singaporean students toward people with disabilities in the general context, as well as the specific social context of dating and marriage. The participants include 212 Taiwanese, 115 Singaporean, and 186 American students. They were given the Attitudes Toward Disabled Persons Scale, Form A (ATDP-A) and the Attitudes Toward Dating and Marriage Scale (ATDMS); the results indicated significant differences between American and Asian students in both the general and specific social contexts. Female American students consistently revealed the most favorable attitudes toward people with disabilities. Implications for cross-cultural rehabilitation practice and research are discussed
The stellar mass - size relation for cluster galaxies at z=1 with high angular resolution from the Gemini/GeMS multi-conjugate adaptive optics system
We present the stellar mass - size relation for 49 galaxies within the =
1.067 cluster SPT-CL J05465345, with FWHM 80-120 mas -band data from the Gemini multi-conjugate adaptive optics system
(GeMS/GSAOI). This is the first such measurement in a cluster environment,
performed at sub-kpc resolution at rest-frame wavelengths dominated by the
light of the underlying old stellar populations. The observed stellar mass -
size relation is offset from the local relation by 0.21 dex, corresponding to a
size evolution proportional to , consistent with the literature.
The slope of the stellar mass - size relation = 0.74 0.06,
consistent with the local relation. The absence of slope evolution indicates
that the amount of size growth is constant with stellar mass. This suggests
that galaxies in massive clusters such as SPT-CL J05465345 grow via
processes that increase the size without significant morphological
interference, such as minor mergers and/or adiabatic expansion. The slope of
the cluster stellar mass - size relation is significantly shallower if measured
in /ACS imaging at wavelengths blueward of the Balmer break, similar to
rest-frame UV relations at = 1 in the literature. The stellar mass - size
relation must be measured at redder wavelengths, which are more sensitive to
the old stellar population that dominates the stellar mass of the galaxies. The
slope is unchanged when GeMS -band imaging is degraded to the resolution
of -band HST/NICMOS resolution but dramatically affected when degraded to
-band Magellan/FourStar resolution. Such measurements must be made with AO
in order to accurately characterise the sizes of compact, = 1 galaxies.Comment: 24 pages, 13 figures, 3 tables. Accepted for publication in MNRAS.
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