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

Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z > 4 Lensed by a Frontier Fields Cluster

We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model (μ = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 10^(10) L_⊙ and an obscured star formation rate of 14.6 ± 4.5 M_⊙ yr^(−1). The unobscured star formation rate from the UV is only 4.1 ± 0.3 M_⊙ yr^(−1), which means the total star formation rate (18.7 ± 4.5 M_⊙ yr^(−1)) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 10^9 M_⊙, MACS0717_Az9 is one of only a handful of z > 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe

Improved photometric redshifts with colour-constrained galaxy templates for future wide-area surveys

Cosmology and galaxy evolution studies with LSST, Euclid, and Roman, will require accurate redshifts for the detected galaxies. In this study, we present improved photometric redshift estimates for galaxies using a template library that populates three-colour space and is constrained by HST/CANDELS photometry. For the training sample, we use a sample of galaxies having photometric redshifts that allows us to train on a large, unbiased galaxy sample having deep, unconfused photometry at optical-to-mid infrared wavelengths. Galaxies in the training sample are assigned to cubes in 3D colour space, V − H, I − J, and z − H. We then derive the best-fitting spectral energy distributions of the training sample at the fixed CANDELS median photometric redshifts to construct the new template library for each individual colour cube (i.e. colour-cube-based template library). We derive photometric redshifts (photo-z) of our target galaxies using our new colour-cube-based template library and with photometry in only a limited set of bands, as expected for the aforementioned surveys. As a result, our method yields σ_(NMAD) of 0.026 and an outlier fraction of 6 per cent using only photometry in the LSST and Euclid/Roman bands. This is an improvement of ∼10 per cent on σ_(NMAD) and a reduction in outlier fraction of ∼13 per cent compared to other techniques. In particular, we improve the photo-z precision by about 30 per cent at 2 < z < 3. We also assess photo-z improvements by including K or mid-infrared bands to the ugrizYJH photometry. Our colour-cube-based template library is a powerful tool to constrain photometric redshifts for future large surveys