SMA Observations on faint submillimeter galaxies with S 850 < 2 mJy: ultra dusty low-luminosity galaxies at high redshift

We obtained Submillimeter Array (SMA) observations of eight faint (intrinsic 850 μm fluxes < 2 mJy) submillimeter galaxies (SMGs) discovered in SCUBA images of the massive lensing cluster fields A370, A2390, and A1689 and detected five. In total, we obtain five SMA detections, all of which have de-lensed fluxes <1 mJy with estimated total infrared luminosities 1010-1012 L ☉, comparable to luminous infrared galaxies and normal star-forming galaxies. Based on the latest number counts, these galaxies contribute ~70% of the 850 μm extragalactic background light and represent the dominant star-forming galaxy population in the dusty universe. However, only 40$^{+30}_{-16}$% of our faint SMGs would be detected in deep optical or near-infrared surveys, which suggests many of these sources are at high redshifts (z gsim 3) or extremely dusty, and they are not included in current star formation history estimates

Tracing the Mass-Assembly History of Galaxies with Deep Surveys

We use the optical and near-infrared galaxy samples from the Munich Near-Infrared Cluster Survey (MUNICS), the FORS Deep Field (FDF) and GOODS-S to probe the stellar mass assembly history of field galaxies out to z ~ 5. Combining information on the galaxies' stellar mass with their star-formation rate and the age of the stellar population, we can draw important conclusions on the assembly of the most massive galaxies in the universe: These objects contain the oldest stellar populations at all redshifts probed. Furthermore, we show that with increasing redshift the contribution of star-formation to the mass assembly for massive galaxies increases dramatically, reaching the era of their formation at z ~ 2 and beyond. These findings can be interpreted as evidence for an early epoch of star formation in the most massive galaxies in the universe.Comment: 3 pages, 2 figures; published in B. Aschenbach, V. Burwitz, G. Hasinger, B. Leibundgut (eds.): "Relativistic Astrophysics and Cosmology - Einstein's Legacy. Proceedings of the Conference held in Munich, 2006", ESO Astrophysics Symposia, Springer Verlag, 2007, p. 310. Replaced to match final published versio

The Host Galaxies of X-ray Quasars Are Not Strong Star Formers

We use ultradeep SCUBA-2 850 μm observations (~0.37 mJy rms) of the 2 Ms Chandra Deep Field-North (CDF-N) and 4 Ms Chandra Deep Field-South X-ray fields to examine the amount of dusty star formation taking place in the host galaxies of high-redshift X-ray active galactic nuclei (AGNs). Supplementing with COSMOS, we measure the submillimeter fluxes of the 4–8 keV sources at $z\gt 1$, finding little flux at the highest X-ray luminosities but significant flux at intermediate luminosities. We determine graybody and MIR luminosities by fitting spectral energy distributions to each X-ray source and to each radio source in an ultradeep Karl G. Jansky Very Large Array (VLA) 1.4 GHz (11.5 μJy at $5\sigma$) image of the CDF-N. We confirm the far-infrared (FIR)-radio and mid-infrared (MIR)-radio correlations to z = 4 using the non-X-ray detected radio sources. Both correlations are also obeyed by the X-ray less luminous AGNs but not by the X-ray quasars. We interpret the low FIR luminosities relative to the MIR for the X-ray quasars as being due to a lack of star formation, while the MIR stays high due to the AGN contribution. We find that the FIR luminosity distributions are highly skewed and the means are dominated by a small number of high-luminosity galaxies. Thus, stacking or averaging analyses will overestimate the level of star formation taking place in the bulk of the X-ray sample. We conclude that most of the host galaxies of X-ray quasars are not strong star formers, perhaps because their star formation is suppressed by AGN feedback

Faint submillimeter galaxy counts at 450 μm

We present the results of SCUBA-2 observations at 450 μm and 850 μm of the field lensed by the massive cluster A370. With a total survey area >100 arcmin2 and 1σ sensitivities of 3.92 and 0.82 mJy beam–1 at 450 and 850 μm, respectively, we find a secure sample of 20 sources at 450 μm and 26 sources at 850 μm with a signal-to-noise ratio (S/N) > 4. Using the latest lensing model of A370 and Monte Carlo simulations, we derive the number counts at both wavelengths. The 450 μm number counts probe a factor of four deeper than the counts recently obtained from the Herschel Space Telescope at similar wavelengths, and we estimate that ~47%-61% of the 450 μm extragalactic background light resolved into individual sources with 450 μm fluxes greater than 4.5 mJy. The faint 450 μm sources in the 4σ sample have positional accuracies of 3 arcsec, while brighter sources (S/N >6σ) are good to 1.4 arcsec. Using a deep radio map (1σ ~ 6 μJy) we find that the percentage of submillimeter sources having secure radio counterparts is 85% for 450 μm sources with intrinsic fluxes >6 mJy and 67% for 850 μm sources with intrinsic fluxes >4 mJy. We also find that 67% of the >4σ 450 μm sources are detected at 850 μm, while the recovery rate at 450 μm of >4σ 850 μm sources is 54%. Combined with the source redshifts estimated using millimetric flux ratios, the recovered rate is consistent with the scenario where both 450 μm and 20 cm emission preferentially select lower redshift dusty sources, while 850 μm emission traces a higher fraction of dusty sources at higher redshifts. We identify potential counterparts in various wavelengths from X-ray to mid-infrared and measure the multiwavelength photometry, which we then use to analyze the characteristics of the sources. We find three X-ray counterparts to our robust submillimeter sample (S/N > 5), giving an active galactic nucleus fraction for our 450 (850) μm sample of 3/8 (3/9) or 38% (33%). We also find a correlation between the Ks band and the 850 μm/20 cm flux ratio

The parallel lives of supermassive black holes and their host galaxies

We compare all the available observational data on the redshift evolution of the total stellar mass and star formation rate density in the Universe with the mass and accretion rate density evolution of supermassive black holes, estimated from the hard X-ray selected luminosity function of quasars and active galactic nuclei. We find that on average black hole mass must have been higher at higher redshift for given spheroid stellar mass. Moreover, we find negative redshift evolution of the disk/irregulars to spheroid mass ratio. The total accretion efficiency is constrained to be between 0.06 and 0.12, depending on the exact value of the local SMBH mass density, and on the critical accretion rate below which radiatively inefficient accretion may take place.Comment: 5 pages, 2 color figures. To appear in the proceedings of "Relativistic Astrophysics and Cosmology - Einstein's Legacy" (Eds.: B. Aschenbach, V. Burwitz, G. Hasinger, and B. Leibundgut), 7 - 11 November 2005, Munich, German

Is there a maximum star formation rate in high-redshift galaxies?

We use the James Clerk Maxwell Telescope's SCUBA-2 camera to image a 400 arcmin2 area surrounding the GOODS-N field. The 850 μm rms noise ranges from a value of 0.49 mJy in the central region to 3.5 mJy at the outside edge. From these data, we construct an 850 μm source catalog to 2 mJy containing 49 sources detected above the 4σ level. We use an ultradeep (11.5 μJy at 5σ) 1.4 GHz image obtained with the Karl G. Jansky Very Large Array together with observations made with the Submillimeter Array to identify counterparts to the submillimeter galaxies. For most cases of multiple radio counterparts, we can identify the correct counterpart from new and existing Submillimeter Array data. We have spectroscopic redshifts for 62% of the radio sources in the 9' radius highest sensitivity region (556/894) and 67% of the radio sources in the GOODS-N region (367/543). We supplement these with a modest number of additional photometric redshifts in the GOODS-N region (30). We measure millimetric redshifts from the radio to submillimeter flux ratios for the unidentified submillimeter sample, assuming an Arp 220 spectral energy distribution. We find a radio-flux-dependent K – z relation for the radio sources, which we use to estimate redshifts for the remaining radio sources. We determine the star formation rates (SFRs) of the submillimeter sources based on their radio powers and their submillimeter fluxes and find that they agree well. The radio data are deep enough to detect star-forming galaxies with SFRs >2000 M ☉ yr–1 to z ~ 6. We find galaxies with SFRs up to ~6000 M ☉ yr–1 over the redshift range z = 1.5-6, but we see evidence for a turn-down in the SFR distribution function above 2000 M ☉ yr–1

A recent rebuilding of most spirals ?

Re-examination of the properties of distant galaxies leads to the evidence that most present-day spirals have built up half of their stellar masses during the last 8 Gyr, mostly during several intense phases of star formation during which they took the appearance of luminous infrared galaxies (LIRGs). Distant galaxy morphologies encompass all of the expected stages of galaxy merging, central core formation and disk growth, while their cores are much bluer than those of present-day bulges. We have tested a spiral rebuilding scenario, for which 75+/-25% of spirals have experienced their last major merger event less than 8 Gyr ago. It accounts for the simultaneous decreases, during that period, of the cosmic star formation density, of the merger rate, of the number densities of LIRGs and of compact galaxies, while the densities of ellipticals and large spirals are essentially unaffected.Comment: (1) GEPI, Obs. Meudon, France ;(2)Max-Planck Institut fuer Astronomie, Germany (3) National Astronomical Observatories, CAS, China. Five pages, 1 figure. To be published in "Starbursts: From 30 Doradus to Lyman Break Galaxies", held in Cambridge, ed. R. de Grijs & R. M. Gonzalez Delgado (Dordrecht: Kluwer

Statistical properties of the GALEX spectroscopic stellar sample

The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more than 60,000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of of stars in the range 4500<Teff<9000 K. Our preliminary results indicate that the sample is formed by a majority of main sequence F- and G-type stars, with metallicity [M/H]>-1 dex.Comment: 9 pages, 9 figures, accepted for publication in Astrophysics & Space Science, UV universe special issu

Photo-z optimization for measurements of the BAO radial direction

Baryon Acoustic Oscillations (BAO) in the radial direction offer a method to directly measure the Universe expansion history, and to set limits to space curvature when combined to the angular BAO signal. In addition to spectroscopic surveys, radial BAO might be measured from accurate enough photometric redshifts obtained with narrow-band filters. We explore the requirements for a photometric survey using Luminous Red Galaxies (LRG) to competitively measure the radial BAO signal and discuss the possible systematic errors of this approach. If LRG were a highly homogeneous population, we show that the photo-z accuracy would not substantially improve by increasing the number of filters beyond $\sim 10$, except for a small fraction of the sources detected at high signal-to-noise, and broad-band filters would suffice to achieve the target $\sigma_z = 0.003 (1+z)$ for measuring radial BAO. Using the LRG spectra obtained from SDSS, we find that the spectral variability of LRG substantially worsens the achievable photometric redshift errors, and that the optimal system consists of $\sim$ 30 filters of width $\Delta \lambda / \lambda \sim 0.02$. A $S/N > 20$ is generally necessary at the filters on the red side of the $H\alpha$ break to reach the target photometric accuracy. We estimate that a 5-year survey in a dedicated telescope with etendue in excess of 60 ${\rm m}^2 {\rm deg}^2$ would be necessary to obtain a high enough density of galaxies to measure radial BAO with sufficiently low shot noise up to $z= 0.85$. We conclude that spectroscopic surveys have a superior performance than photometric ones for measuring BAO in the radial direction.Comment: Replaced with minor editorial comments and one extra figure. Results unchange

Time Variations in the Scale of Grand Unification

We study the consequences of time variations in the scale of grand unification, $M_U$, when the Planck scale and the value of the unified coupling at the Planck scale are held fixed. We show that the relation between the variations of the low energy gauge couplings is highly model dependent. It is even possible, in principle, that the electromagnetic coupling $\alpha$ varies, but the strong coupling $\alpha_3$ does not (to leading approximation). We investigate whether the interpretation of recent observations of quasar absorption lines in terms of time variation in $\alpha$ can be accounted for by time variation in $M_U$. Our formalism can be applied to any scenario where a time variation in an intermediate scale induces, through threshold corrections, time variations in the effective low scale couplings.Comment: 14 pages, revtex4; Updated observational results and improved statistical analysis (section IV); added reference