103 research outputs found
Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies
We study the infrared (IR) properties of high-redshift galaxies using deep
Spitzer 24, 70, and 160 micron data. Our primary interest is to improve the
constraints on the total IR luminosities, L(IR), of these galaxies. We combine
the Spitzer data in the southern Extended Chandra Deep Field with a
K-band-selected galaxy sample and photometric redshifts from the
Multiwavelength Survey by Yale-Chile. We used a stacking analysis to measure
the average 70 and 160 micron flux densities of 1.5 < z < 2.5 galaxies as a
function of 24 micron flux density, X-ray activity, and rest-frame near-IR
color. Galaxies with 1.5 < z < 2.5 and S(24)=53-250 micro-Jy have L(IR) derived
from their average 24-160 micron flux densities within factors of 2-3 of those
derived from the 24 micron flux densities only. However, L(IR) derived from the
average 24-160 micron flux densities for galaxies with S(24) > 250 micro-Jy and
1.5 < z < 2.5 are lower than those derived using only the 24 micron flux
density by factors of 2-10. Galaxies with S(24) > 250 micro-Jy have S(70)/S(24)
flux ratios comparable to sources with X-ray detections or red rest-frame IR
colors, suggesting that warm dust possibly heated by AGN may contribute to the
high 24 micron emission. Based on the average 24-160 micron flux densities,
nearly all 24 micron-selected galaxies at 1.5 < z < 2.5 have L(IR) < 6 x 10^12
solar luminosities, which if attributed to star formation corresponds to < 1000
solar masses per year. This suggests that high redshift galaxies may have
similar star formation efficiencies and feedback processes as local analogs.
Objects with L(IR) > 6 x 10^12 solar luminosities are quite rare, with a
surface density ~ 30 +/- 10 per sq. deg, corresponding to ~ 2 +/- 1 x 10^-6
Mpc^-3 over 1.5 < z < 2.5.Comment: Accepted for Publication in ApJ. AASTeX format. 34 pages, 12 figures.
Updated references and other small textual revision
Spitzer view on the evolution of star-forming galaxies from z=0 to z~3
We use a 24 micron selected sample containing more than 8,000 sources to
study the evolution of star-forming galaxies in the redshift range from z=0 to
z~3. We obtain photometric redshifts for most of the sources in our survey
using a method based on empirically-built templates spanning from ultraviolet
to mid-infrared wavelengths. The accuracy of these redshifts is better than 10%
for 80% of the sample. The derived redshift distribution of the sources
detected by our survey peaks at around z=0.6-1.0 (the location of the peak
being affected by cosmic variance), and decays monotonically from z~1 to z~3.
We have fitted infrared luminosity functions in several redshift bins in the
range 0<z<~3. Our results constrain the density and/or luminosity evolution of
infrared-bright star-forming galaxies. The typical infrared luminosity (L*)
decreases by an order of magnitude from z~2 to the present. The cosmic star
formation rate (SFR) density goes as (1+z)^{4.0\pm0.2} from z=0 to z=0.8. From
z=0.8 to z~1.2, the SFR density continues rising with a smaller slope. At
1.2<z<3, the cosmic SFR density remains roughly constant. The SFR density is
dominated at low redshift (z<0.5) by galaxies which are not very luminous in
the infrared (L_TIR<1.e11 L_sun, where L_TIR is the total infrared luminosity,
integrated from 8 to 1000 micron). The contribution from luminous and
ultraluminous infrared galaxies (L_TIR>1.e11 L_sun) to the total SFR density
increases steadily from z~0 up to z~2.5, forming at least half of the
newly-born stars by z~1.5. Ultraluminous infrared galaxies (L_TIR>1.e12 L_sun)
play a rapidly increasing role for z>~1.3.Comment: 28 pages, 17 figures, accepted for publication in Ap
Synthetic Studies in Phytochrome Chemistry
An account is given of the authorâs several approaches to the synthesis of the parent chromophore of phytochrome (1), a protein-bound linear tetrapyrrole derivative that controls photomorphogenesis in higher plants. These studies culminated in enantioselective syntheses of both (2R)- and (2S)-phytochromobilin (4), as well as several 13C-labeled derivatives designed to probe the site of Z,E-isomerization during photoexcitation. When reacted in vitro, synthetic 2R-4 and recombinant-derived phytochrome apoprotein N-C produced a protein-bound chromophore with identical difference spectra to naturally occurring 1
Herschel Observations of Major Merger Pairs at z=0: Dust Mass and Star Formation
We present Herschel PACS and SPIRE far-infrared (FIR) and submillimeter imaging observations for a large K-band selected sample of 88 close major-merger pairs of galaxies (H-KPAIRs) in 6 photometric bands (70, 100, 160, 250, 350, and 500 ÎŒm). Among 132 spiral galaxies in the 44 spiralâspiral (S+S) pairs and 44 spiralâelliptical (S+E) pairs, 113 are detected in at least 1 Herschel band. The star formation rate (SFR) and dust mass (M_(dust)) are derived from the IR SED fitting. The mass of total gas (M_(gas)) is estimated by assuming a constant dust-to-gas mass ratio of 0.01. Star-forming spiral galaxies (SFGs) in S+S pairs show significant enhancements in both specific star formation rate (sSFR) and star formation efficiency (SFE), while having nearly the same gas mass compared to control galaxies. On the other hand, for SFGs in S+E pairs, there is no significant sSFR enhancement and the mean SFE enhancement is significantly lower than that of SFGs in S+S pairs. This suggests an important role for the diskâdisk collision in the interaction-induced star formation. The M_(gas) of SFGs in S+E pairs is marginally lower than that of their counterparts in both S+S pairs and the control sample. Paired galaxies with and without interaction signs do not differ significantly in their mean sSFR and SFE. As found in previous works, this much larger sample confirms that the primary and secondary spirals in S+S pairs follow a Holmberg effect correlation on sSFR
The Carotid and Middle cerebral artery Occlusion Surgery Study (CMOSS): a study protocol for a randomised controlled trial
An Extreme Starburst in the Core of a Rich Galaxy Cluster at z = 1.7
We have discovered an optically rich galaxy cluster at z = 1.7089 with star formation occurring in close proximity to the central galaxy. The system, SpARCS104922.6+564032.5, was detected within the Spitzer Adaptation of the red-sequence Cluster Survey, and confirmed through Keck-MOSFIRE spectroscopy. The rest-frame optical richness of N_(gal) (500 kpc) = 30 ± 8 implies a total halo mass, within 500 kpc, of ~3.8 ± 1.2 Ă 10^(14) Mâ, comparable to other clusters at or above this redshift. There is a wealth of ancillary data available, including CanadaâFranceâHawaii Telescope optical, UKIRT-K, Spitzer-IRAC/MIPS, and Herschel-SPIRE. This work adds submillimeter imaging with the SCUBA2 camera on the James Clerk Maxwell Telescope and near-infrared imaging with the Hubble Space Telescope. The mid/far-infrared (M/FIR) data detect an Ultra-luminous Infrared Galaxy spatially coincident with the central galaxy, with L_(IR) = 6.2 ± 0.9 Ă 10^(12) Lâ. The detection of polycyclic aromatic hydrocarbons at z = 1.7 in a Spitzer-IRS spectrum of the source implies the FIR luminosity is dominated by star formation (an Active Galactic Nucleus contribution of 20%) with a rate of ~860 ± 130 Mâ yr^(â1). The optical source corresponding to the IR emission is likely a chain of >10 individual clumps arranged as "beads on a string" over a linear scale of 66 kpc. Its morphology and proximity to the Brightest Cluster Galaxy (BCG) imply a gas-rich interaction at the center of the cluster triggered the star formation. This system indicates that wet mergers may be an important process in forming the stellar mass of BCGs at early times
Oridonin induces apoptosis and cell cycle arrest of gallbladder cancer cells via the mitochondrial pathway
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