We investigate the relation between star formation rates (
$\dot{{M}}_s$
) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that
...$\dot{{M}}_s$
remains approximately constant with redshift, at 300 ± 100 M⊙ yr−1. Conversely,
$\dot{{M}}_s$
increases with AGN luminosity, up to a maximum of ∼ 600 M⊙ yr−1, and with C iv FWHM. In context with previous results, this is consistent with a relation between
$\dot{{M}}_s$
and black hole accretion rate (
$\dot{{M}}_{{\rm bh}}$
) existing in only parts of the
$z-\dot{{M}}_{s}-\dot{{M}}_{{\rm bh}}$
plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between
$\dot{{M}}_s$
and both AGN luminosity and C iv FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C iv equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; M
i
is not a linear tracer of L
2500, the Baldwin effect changes form at high AGN luminosities, and high C iv EW values signpost a change in the relation between
$\dot{{M}}_s$
and
$\dot{{M}}_{{\rm bh}}$
. Finally, there is no strong relation between
$\dot{{M}}_s$
and Eddington ratio, or the asymmetry of the C iv line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C iv asymmetries arising from orientation effects.
We characterize the incidence of active galactic nuclei (AGNs) in 0.3 < z < 1 star-forming galaxies by applying multi-wavelength AGN diagnostics (X-ray, optical, mid-infrared, radio) to a sample of ...galaxies selected at 70 mu m from the Far-Infrared Deep Extragalactic Legacy survey (FIDEL). Given the depth of FIDEL, we detect "normal" galaxies on the specific star formation rate (sSFR) sequence as well as starbursting systems with elevated sSFR. We find an overall high occurrence of AGN of 37% + or - 3%, more than twice as high as in previous studies of galaxies with comparable infrared luminosities and redshifts but in good agreement with the AGN fraction of nearby (0.05 < z < 0.1) galaxies of similar infrared luminosities. The more complete census of AGNs comes from using the recently developed Mass-Excitation (MEx) diagnostic diagram. This optical diagnostic is also sensitive to X-ray weak AGNs and X-ray absorbed AGNs, and reveals that absorbed active nuclei reside almost exclusively in infrared-luminous hosts. The fraction of galaxies hosting an AGN appears to be independent of sSFR and remains elevated both on the sSFR sequence and above. In contrast, the fraction of AGNs that are X-ray absorbed increases substantially with increasing sSFR, possibly due to an increased gas fraction and/or gas density in the host galaxies.
We aim to measure the average dust and molecular gas content of massive star-forming galaxies (>3 × 1010M⊙) up to z = 4 in the COSMOS field to determine if the intense star formation observed at high ...redshift is induced by major mergers or is caused by large gas reservoirs. Firstly, we measured the evolution of the average spectral energy distributions as a function of redshift using a stacking analysis of Spitzer, Herschel, LABOCA, and AzTEC data for two samples of galaxies: normal star-forming objects and strong starbursts, as defined by their distance to the main sequence. We found that the mean intensity of the radiation field ⟨ U ⟩ heating the dust (strongly correlated with dust temperature) increases with increasing redshift up to z = 4 in main-sequence galaxies. We can reproduce this evolution with simple models that account for the decrease in the gas metallicity with redshift. No evolution of ⟨ U ⟩ with redshift is found in strong starbursts. We then deduced the evolution of the molecular gas fraction (defined here as Mmol/ (Mmol + M⋆)) with redshift and found a similar, steeply increasing trend for both samples. At z ~ 4, this fraction reaches ~60%. The average position of the main-sequence galaxies is on the locus of the local, normal star-forming disks in the integrated Schmidt-Kennicutt diagram (star formation rate versus mass of molecular gas), suggesting that the bulk of the star formation up to z = 4 is dominated by secular processes.
Full text
Available for:
FMFMET, NUK, UL, UM, UPUK
We present the first cross-correlation measurement between Sloan Digital Sky Survey type 1 quasars and the cosmic infrared background (CIB) measured by Herschel. The quasars cover the redshift range ...0.15 < z < 3.5 where most of the CIB originates. We detect the sub-millimetre emission of the quasars, which dominates on small scales, and correlated emission from dusty star-forming galaxies (DSFGs) dominant on larger scales. The mean flux of the Data Release 7 (DR7) quasars (median redshift 〈z〉 = 1.4) is 11.1, 7.1 and 3.6 mJy at 250, 350 and 500 μm, respectively, while the mean flux of the DR9 quasars (〈z〉 = 2.5) is 5.7, 5.0 and 1.8 mJy at 250, 350 and 500 μm, respectively. Assuming a modified blackbody spectral energy distribution with a power law in the mid-infrared, we infer that the mean infrared luminosity of the DR7 and DR9 quasars is 1012.4 and 1012.8 L⊙, respectively. The correlated emission arises from DSFGs in the same halo as the quasar (the one-halo term) and DSFGs in separate haloes correlated with the quasar-hosting halo (the two-halo term). Using a simple halo model, we find that most quasars are hosted by central galaxies. The host halo mass scale of the DR7 central and satellite quasars is 1012.4 ± 0.9 and 1013.6 ± 0.4 M⊙, respectively. The host halo mass scale of the DR9 central and satellite quasars is 1012.3 ± 0.6 and 1012.8 ± 0.4 M⊙, respectively. Thus, the halo environment of the central quasars is similar to that of the most actively star-forming galaxies, which supports the view that dusty starburst and quasar activity are evolutionarily linked.
A POPULATION OF DUST-RICH QUASARS AT z ∼ 1.5 SOPHIA DAI, Y; BERGERON, Jacqueline; MAGDIS, Georgios E ...
The Astrophysical journal,
07/2012, Volume:
753, Issue:
1
Journal Article
Peer reviewed
We report Herschel SPIRE (250, 350, and 500 mu m) detections of 32 quasars with redshifts 0.5 < or =, slant z < 3.6 from the Herschel Multi-tiered Extragalactic Survey (HerMES). These sources are ...from a MIPS 24 mu m flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame spectral energy distributions (SEDs) from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25-60 K, with a mean of 34 K. The FIR luminosities range from 10 super(11.3) to 10 super(13.5) L sub(middot in circle), qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ~1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3-20 mu m, rest frame), and the bolometric luminosities derived using the 5100 Angstrom index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities.
The AGN. I examine the average spectral energy distributions (SEDs) of two samples of the most powerful, unobscured QSOs at 2<z<3.5, with rest frame optical luminosities in the 46.2<log ...vLv(5100Ang)<47.4 range, corresponding to the tail of the 2<z<4 QSO optical luminosity function. I find that the AGN could potentially account for the entire broad-band emission from the UV to the submm, on the basis that the SEDs of these sources are similar to the intrinsic AGN SEDs derived for lower power, lower redshift QSOs. Although this does not preclude substantial star-formation in their host galaxies, I find that the AGN dominates the total infrared luminosity, removing the necessity for a star-forming component in the far-IR/submm. I argue that the origin of the far-IR/submm emission in such powerful QSOs includes a small contribution from the AGN torus, but is predominantly linked to dust at kpc-scales heated by the AGN. The latter component accounts for at least 5-10 per cent of the bolometric AGN luminosity and has an implied dust mass of the order of 10^8 solar masses.
We investigate what shapes the infrared luminosity function of local galaxies by comparing it to the local infrared AGN luminosity function. The former corresponds to emission from dust heated by ...stars and AGN, whereas the latter includes emission from AGN-heated dust only. Our results show that infrared emission from AGN starts mixing into the galaxy luminosity function in the luminous infrared galaxy (LIRG) regime and becomes significant in the ultraluminous infrared galaxy (ULIRG) regime, with the luminosity above which local ULIRGs become AGN-dominated being in the log(LIR/Lsun)~12.2-12.7 range. We propose that as a result of the AGN contribution, the infrared galaxy luminosity function has a flatter high luminosity slope than UV/optical galaxy luminosity functions. Furthermore, we note that the increased AGN contribution as a function of LIR is reflected in the average dust temperature (Tdust) of local galaxies, and may be responsible for the local LIR-Tdust relation. However, although our results show that AGN play a central role in defining the properties of local ULIRGs, we find that the dominant power source in the local ULIRG population is star-formation.
SWIFT is an adaptive optics assisted integral field spectrograph covering the I and z astronomical bands (0.7–1.0μm) at a spectral resolving power R⩽5000. At its heart is an all-glass image slicer ...with high throughput based on a novel de-magnifying design allowing a compact instrument. SWIFT profits from two recent developments: (i) the improved ability of second generation adaptive optics systems to correct for atmospheric turbulence in SWIFTS’s bandpass, and (ii) the availability of CCD array detectors with high quantum efficiency at very red wavelengths. It is a dedicated integral field spectrograph, specifically built to address a range of interesting astrophysical questions.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
AIM： To detect the prevalence of anti-HAV IgG antibodies in adult multitransfused beta-thalassemic patients. METHODS： We studied 182 adult beta-thalassemic patients and 209 controls matched for age ...and sex from the same geographic area, at the same time. Anti-HAV IgG antibodies, viral markers of hepatitis B virus （HBV） and hepatitis C virus （HCV） infection were evaluated. RESULTS： Anti-HAV IgG antibodies were detected more frequently in thalassemic patients （133/182; 73.1%） than in healthy controls （38/209; 18.2%, P 〈 0.0005）. When we retrospectively evaluated the prevalence of anti-HAV IgG antibodies in 176/182 （96.7%） thalassemic patients, whose medical history was available for the previous ten years, it was found that 83 （47.2%） of them were continuously anti-HAV IgG positive, 16 （9.1%） acquired anti-HAV IgG antibody during the previous ten years, 49 （27.8%） presented anti-HAV positivity intermittently and 28 （15.9%） were anti-HAV negative continuously. CONCLUSION： Multitransfused adult beta-thalassemic patients present higher frequency of anti-HAV IgG antibodies than normal population of the same geographic area. This difference is difficult to explain, but it can be attributed to the higher vulnerability of thalassemics to HAV infection and to passive transfer of anti-HAV antibodies by blood transfusions.
PDF
