Arp102B: An ADAF and a Torus ?

Arp102B is a nearby radio galaxy which displays the presence of double peaked Balmer emission lines. Sub-arcsec Keck mid-infrared imaging and Spitzer spectroscopy reveal a spatially compact mid-infrared source which displays tentative evidence for variability. The F$_{\nu}\propto\nu^{-1.2}$ spectral energy distribution is suggestive of an advection dominated accretion flow. The absence of dust features over the 5-40 micron range make it unlikely that thermal dust emission dominates the mid-infrared luminosity. We also detect the presence of molecular hydrogen in emission which is asymmetrically redshifted by ~500-1000 km/s from the systemic velocity of the galaxy. Since the forbidden, low ionization lines in this galaxy are at the systemic velocity, we suggest that the molecular hydrogen emission arises from a rotating molecular gas structure surrounding the nuclear black hole at a distance of ~1 pc.Comment: 4 pages, 3 figures, Conference proceedings to appear in "The Central Engine of Active Galactic Nuclei", ed. L. C. Ho and J.-M. Wang (San Francisco: ASP

Insights into galaxy evolution from mid-infrared wavelengths

In this paper, I have attempted to highlight key results from deep extragalactic surveys at mid-infrared wavelengths. I discuss advances in our understanding of dust enshrouded star-formation and AGN activity at 0 3 will become possible only with future facilities like ALMA. Currently, the presence of dust can only be assessed in a small fraction of the youngest starbursts at z > 5 by looking for redshifted large equivalent width Hα emission in broadband filters like the IRAC 4.5μm passband. Hα to UV ratios in these objects are a tracer of dust extinction and measuring this ratio in GOODS galaxies indicate dust in ~20% of star-forming galaxies at z > 5. Finally, implications for reionization based on the measured stellar mass density and star-formation rates of galaxies at these redshifts are discussed

Unveiling the Progenitors of GRBs through Observations of their Host Galaxies

I discuss the possibility of differentiating between popular models for gamma-ray bursts by using multiwavelength observations to constrain the characteristics of their host galaxies, in particular the age of the stellar populations.Comment: 3 pages, Proceedings of "Gamma-Ray Burst and Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE Mission", AI

Searching for the Highest Redshift Sources in 250-500 μm Submillimeter Surveys

We explore a technique for identifying the highest redshift (z>4) sources in Herschel/SPIRE and BLAST submillimeter surveys by localizing the position of the far-infrared dust peak. Just as Spitzer/IRAC was used to identify stellar "bump" sources, the far-IR peak is also a redshift indicator; although the latter also depends on the average dust temperature. We demonstrate the wide range of allowable redshifts for a reasonable range of dust temperatures and show that it is impossible to constraint the redshift of individual objects using solely the position of the far-IR peak. By fitting spectral energy distribution models to simulated Herschel/SPIRE photometry we show the utility of radio and/or far-infrared data in breaking this degeneracy. With prior knowledge of the dust temperature distribution it is possible to obtain statistical samples of high redshift submillimeter galaxy (SMG) candidates. We apply this technique to the BLAST survey of ECDFS to constrain the number of dusty galaxies at z>4. We find 8 ± 2 galaxies with flux density ratios of S_(500)_>S_(350); this sets an upper limit of 17 ± 4 deg^(–2) if we assume all are at z>4. This is 45 mJy (L_(IR)>2 × 10^(13) L_☉ for z>4). Modeling with conventional temperature and redshift distributions estimates the percentage of these 500 μm peak galaxies at z>4 to be between 10% and 85%. Our results are consistent with other estimates of the number density of very high redshift SMGs and follow the decline in the star formation rate density at z>4

Exploring the Galaxy Mass-Metallicity Relations at z ~ 3-5

Long-duration gamma-ray bursts (GRBs) provide a premier tool for studying high-redshift star-forming galaxies thanks to their extreme brightness and association with massive stars. Here we use GRBs to study the galaxy stellar mass-metallicity (M_*-Z) relation at z ~ 3-5, where conventional direct metallicity measurements are extremely challenging. We use the interstellar medium metallicities of long GRB hosts derived from afterglow absorption spectroscopy, in conjunction with host galaxy stellar masses determined from deep Spitzer 3.6 μm observations of 20 GRB hosts. We detect about 1/4 of the hosts with M_(AB)(I) ≈ –21.5 to –22.5 mag and place a limit of M_(AB)(I) ≳ –19 mag on the remaining hosts from a stacking analysis. Using these observations, we present the first rest-frame optical luminosity distribution of long GRB hosts at z ≳ 3 and find that it is similar to the distribution of long GRB hosts at z ~ 1. In comparison to Lyman-break galaxies at the same redshift, GRB hosts are generally fainter, but the sample is too small to rule out an overall similar luminosity function. On the other hand, the GRB hosts appear to be more luminous than the population of Lyα emitters at z ~ 3-4. Using a conservative range of mass-to-light ratios for simple stellar populations (with ages of 70 Myr to ~2 Gyr), we infer the host stellar masses and present mass-metallicity measurements at z ~ 3-5 ((z) ≈ 3.5). We find that the detected GRB hosts, with M_* ≈ 2 × 10^(10) M_☉, display a wide range of metallicities, but that the mean metallicity at this mass scale, Z ≈ 0.3 Z_☉, is lower than measurements at z ≾ 3. Combined with stacking of the non-detected hosts with M_* ≾ 3 × 10^9 M_☉ and Z ≾ 0.1 Z_☉, we find tentative evidence for the existence of an M_*-Z relation at z ~ 3.5 and continued evolution of this relation to systematically lower metallicities from z ~ 2

CARMA observations of massive Planck-discovered cluster candidates at z>0.5 associated with WISE overdensities: strategy, observations and validation

We present 1-2 arcmin spatial resolution CARMA-8 31-GHz observations towards 19 unconfirmed Planck cluster candidates, selected to have significant galaxy overdensities from the WISE early data release and thought to be at z>1 from the WISE colors of the putative brightest cluster galaxy (BCG). We find a Sunyaev-Zeldovich (SZ) detection in the CARMA-8 data towards 9 candidate clusters, where one detection is considered tentative. For each cluster candidate we present CARMA-8 maps, a study of their radio-source environment and we assess the reliability of the SZ detection. The CARMA SZ detections appear to be SZ-bright, with the mean, primary-beam-corrected peak flux density of the decrement being -2.9mJy/beam with a standard deviation of 0.8, and are typically offset from the Planck position by approximately 80 arcsec. Using archival imaging data in the vicinity of the CARMA SZ centroids, we present evidence that one cluster matches Abell 586-a known z~0.2 cluster; four candidate clusters are likely to have 0.3<z<0.7; and, for the remaining 4, the redshift information is inconclusive. We also argue that the sensitivity limits resulting from the cross-correlation between Planck and WISE makes it challenging to use our selection criterion to identify clusters at z > 1.Comment: 29 pages, MNRAS, in pres

The Stellar Initial Mass Function at the Epoch of Reionization

I provide estimates of the ultraviolet and visible light luminosity density at z~6 after accounting for the contribution from faint galaxies below the detection limit of deep Hubble and Spitzer surveys. I find the rest-frame V-band luminosity density is a factor of ~2-3 below the ultraviolet luminosity density at z~6. This implies that the maximal age of the stellar population at z~6, for a Salpeter initial mass function, and a single, passively evolving burst, must be <100 Myr. If the stars in z~6 galaxies are remnants of the star-formation that was responsible for ionizing the intergalactic medium, reionization must have been a brief process that was completed at z<7. This assumes the most current estimates of the clumping factor and escape fraction and a Salpeter slope extending up to 200 M_{\sun} for the stellar initial mass function (IMF; dN/dM \propto M^{\alpha}, \alpha=-2.3). Unless the ratio of the clumping factor to escape fraction is less than 60, a Salpeter slope for the stellar IMF and reionization redshift higher than 7 is ruled out. In order to maintain an ionized intergalactic medium from redshift 9 onwards, the stellar IMF must have a slope of \alpha=-1.65 even if stars as massive as ~200 M_{\sun} are formed. Correspondingly, if the intergalactic medium was ionized from redshift 11 onwards, the IMF must have \alpha~-1.5. The range of stellar mass densities at z~6 straddled by IMFs which result in reionization at z>7 is 1.3+/-0.4\times10^{7} Msun/Mpc^3.Comment: 25 pages, 2 tables, 6 figures, ApJ, in press, v680 n