Kinematically Identified Recoiling Supermassive Black Hole Candidates in SDSS QSOs with z << 0.25

We have performed a spectral decomposition to search for recoiling supermassive black holes (rSMBH) in the SDSS QSOs with $z<0.25$. Out of 1271 QSOs, we have identified 26 rSMBH candidates that are recoiling toward us. The projected recoil velocities range from -76\ \kms to -307\ \kms with a mean of -149\pm58\ \kms. Most of the rSMBH candidates are hosted by gas-rich LIRGs/ULIRGs, but only 23\% of them shows signs of tidal features suggesting majority of them are advanced mergers. We find that the black hole masses $M_{BH}$ of the rSMBH candidates are on average $\sim$5 times smaller than that of their stationary counterparts and cause a scatter in $M_{BH}-\sigma_*$ relation. The Eddington ratios of all of the rSMBH candidates are larger than 0.1, with mean of 0.52$\pm$0.27, suggesting they are actively accreting mass. Velocity shifts in high-excitation coronal lines suggest that the rSMBH candidates are recoiling with an average velocity of about -265\ \kms. Electron density in the narrow line region of the H II rSMBH candidates is about 1/10 of that in AGN rSMBH candidates probably because AGN in the former was more spatially offset than that in the latter. The estimated spatial offsets between the rSMBH candidate and center of host galaxy range from 0.21\as \ to 1.97\as \ and need to be confirmed spatially with high-resolution adaptive optics imaging observations.Comment: ApJ accepte

The Arecibo Legacy Fast ALFA Survey: VIII. HI Source Catalog of the Anti-Virgo Region at dec = +25 deg

We present a fourth catalog of HI sources from the Arecibo Legacy Fast ALFA (ALFALFA) Survey. We report 541 detections over 136 deg2, within the region of the sky having 22h < R.A. < 03h and 24 deg < Dec. < 26 deg . This complements a previous catalog in the region 26 deg < Dec. < 28 deg (Saintonge et al. 2008). We present here the detections falling into three classes: (a) extragalactic sources with S/N > 6.5, where the reliability of the catalog is better than 95%; (b) extragalactic sources 5.0 < S/N < 6.5 and a previously measured optical redshift that corroborates our detection; or (c) High Velocity Clouds (HVCs), or subcomponents of such clouds, in the periphery of the Milky Way. Of the 541 objects presented here, 90 are associated with High Velocity Clouds, while the remaining 451 are identified as extragalactic objects. Optical counterparts have been matched with all but one of the extragalactic objects.Comment: 26 pages, 5 figures, 1 table, accepted for publication in Astrophysical Journal Supplement Serie

The Weak Carbon Monoxide Emission In An Extremely Metal Poor Galaxy, Sextans A

Carbon monoxide (CO) is one of the primary coolants of gas and an easily accessible tracer of molecular gas in spiral galaxies but it is unclear if CO plays a similar role in metal poor dwarfs. We carried out a deep observation with IRAM 30 m to search for CO emission by targeting the brightest far-IR peak in a nearby extremely metal poor galaxy, Sextans A, with 7% Solar metallicity. A weak CO J=1-0 emission is seen, which is already faint enough to place a strong constraint on the conversion factor (a_CO) from the CO luminosity to the molecular gas mass that is derived from the spatially resolved dust mass map. The a_CO is at least seven hundred times the Milky Way value. This indicates that CO emission is exceedingly weak in extremely metal poor galaxies, challenging its role as a coolant in these galaxies.Comment: 4 pages, 1 table, 4 figures. ApJL in pres

Inefficient Star Formation In Extremely Metal Poor Galaxies

The first galaxies contain stars born out of gas with little or no metals. The lack of metals is expected to inhibit efficient gas cooling and star formation but this effect has yet to be observed in galaxies with oxygen abundance relative to hydrogen below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon Monoxide (CO) emission is unreliable as tracers of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low-spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially-resolved infrared observations of two galaxies with oxygen abundances below 10 per cent solar, and show that stars form very inefficiently in seven star-forming clumps of these galaxies. The star formation efficiencies are more than ten times lower than found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe.Comment: Author's version (10 pages, 4 figures). Published in Natur

Spatially resolved dust emission of extremely metal poor galaxies

We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal poor (EMP) galaxies with metallicity Z around Zsun/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70um/f160um ratios at a given f160um/f250um ratio; single modified black-body (MBB) fittings to the SED at \lambda >= 100 um still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (beta = 2) show that even at 100 um about half of the emission comes from warm (50 K) dust, in contrast to the cold (~20 K) dust component. Our spatially resolved images further reveal that the far-IR colors including f70um/f160um, f160um/f250um and f250um/f350um are all related to the surface densities of young stars as traced by far-UV, 24 um and SFRs, but not to the stellar mass surface densities. This suggests that the dust emitting at wavelengths from 70 um to 350 um is primarily heated by radiation from young stars.Comment: 9 pages, 7 figures, 7 tables, accepted for publication in MNRA

A Joint Model of the X-Ray and Infrared Extragalactic Backgrounds. I. Model Construction and First Results

We present an extragalactic population model of the cosmic background light to interpret the rich high-quality survey data in the X-ray and IR bands. The model incorporates star formation and supermassive black hole (SMBH) accretion in a co-evolution scenario to fit simultaneously 617 data points of number counts, redshift distributions, and local luminosity functions (LFs) with 19 free parameters. The model has four main components, the total IR LF, the SMBH accretion energy fraction in the IR band, the star formation spectral energy distribution (SED), and the unobscured SMBH SED extinguished with a H I column density distribution. As a result of the observational uncertainties about the star formation and SMBH SEDs, we present several variants of the model. The best-fit reduced χ2 reaches as small as 2.7-2.9 of which a significant amount (>0.8) is contributed by cosmic variances or caveats associated with data. Compared to previous models, the unique result of this model is to constrain the SMBH energy fraction in the IR band that is found to increase with the IR luminosity but decrease with redshift up to z ~ 1.5; this result is separately verified using aromatic feature equivalent-width data. The joint modeling of X-ray and mid-IR data allows for improved constraints on the obscured active galactic nucleus (AGN), especially the Compton-thick AGN population. All variants of the model require that Compton-thick AGN fractions decrease with the SMBH luminosity but increase with redshift while the type 1 AGN fraction has the reverse trend