Lusine A. Sargsyan

Infrared Spectra and Spectral Energy Distributions for Dusty Starbursts and Active Galactic Nuclei

We present spectroscopic results for all galaxies observed with the Spitzer Infrared Spectrograph (IRS) that also have total infrared fluxes f IR measured with the Infrared Astronomical Satellite (IRAS), also using AKARI photometry when available. Infrared luminosities and spectral energy distributions (SEDs) from 8 μm to 160 μm are compared to polycyclic aromatic hydrocarbon emission from starburst galaxies or mid-infrared dust continuum from active galactic nuclei (AGNs) at rest-frame wavelengths ~8 μm. A total of 301 spectra are analyzed for which IRS and IRAS include the same unresolved source, as measured by the ratio f ν(IRAS 25 μm)/f ν(IRS 25 μm). Sources have 0.004 < z < 0.34 and 42.5 < log L IR < 46.8 (erg s–1) and cover the full range of starburst galaxy and AGN classifications. Individual spectra are provided electronically, but averages and dispersions are presented. We find that log [L IR/νL ν(7.7 μm)] = 0.74 ± 0.18 in starbursts, log [L IR/νL ν(7.7 μm)] = 0.96 ± 0.26 in composite sources (starburst plus AGN), log [L IR/νL ν(7.9 μm)] = 0.80 ± 0.25 in AGNs with silicate absorption, and that log [L IR/νL ν(7.9 μm)] = 0.51 ± 0.21 in AGNs with silicate emission. L IR for the most luminous absorption and emission AGNs are similar and 2.5 times larger than for the most luminous starbursts. AGNs have systematically flatter SEDs than starbursts or composites, but their dispersion in SEDs overlaps starbursts. Sources with the strongest far-infrared luminosity from cool dust components are composite sources, indicating that these sources may contain the most obscured starbursts.

The digitized first Byurakan survey - DFBS

Context. The First Byurakan Survey (FBS), also known as the Markarian Survey, is the largest low resolution spectroscopic survey of the sky and led to the discovery of 1500 UV-excess (UVX) galaxies and starburst galaxies. The FBS plates have also been used to search for UVX stellar objects, late-type stars, and for the identification of unusual infrared sources. Aims. The Digitized First Byurakan Survey (DFBS) provides the astronomical community with a digitized version of the FBS images and with the extracted spectra for the objects present in the plates. Methods. Nearly 2000 plates have been scanned and stored and programs were developed to compute the astrometric solution, extract the spectra, and apply wavelength and photometric calibration for the objects present in the plates. Results. The DFBS database and catalog of objects has been assembled. The DFBS database contains data for 20 000 000 objects present in the survey and provides tools for accessing the DFBS. Conclusions. New scientific projects as well as existing surveys will benefit by the digitized images and the ready-to-use extracted spectra which will allow an efficient computer-based analysis of the dataset.

STAR FORMATION RATES FOR STARBURST GALAXIES FROM ULTRAVIOLET, INFRARED, AND RADIO LUMINOSITIES

We present a comparison of star formation rates (SFR) determined from mid-infrared 7.7 μm polycyclic aromatic hydrocarbon (PAH) luminosity [SFR(PAH)], from 1.4 GHz radio luminosity [SFR(radio)], and from far-ultraviolet luminosity [SFR(UV)] for a sample of 287 starburst galaxies with z 700 for the most luminous starbursts at z ~ 2.5. Application of this factor explains why the most luminous starbursts discovered by Spitzer at z ~ 2.5 are optically faint; with this amount of extinction, the optical magnitude of a starburst having f ν(7.7 μm) of 1 mJy should be V~ 25.6.

Spitzer IRS Spectra of Optically Faint IRAS Sources

Extragalactic sources from the IRAS Faint Source Catalog (FSC) that have the optically faintest magnitudes (E 18) were selected by spatial coincidence with a source in the FIRST radio survey, and 28 of these sources have been observed with the Infrared Spectrograph on Spitzer (IRS). While an infrared source is always detected with the IRS at the FIRST position, only ~50% of the infrared sources are real FSC detections, as estimated from the number of sources for which the fν(25 μm) determined with the IRS is fainter than the sensitivity limit for the FSC. Sources have 0.12 < z < 1.0 and luminosities (ergs s−1) 43.3 < log [ ν Lν(5.5 μ m) ] < 46.7, encompassing the range from local ULIRGs to the most luminous sources discovered by Spitzer at z ~ 2. Detectable PAH features are found in 15 of the sources (54%), and measurable silicate absorption is found in 19 sources (68%); both PAH emission and silicate absorption are present in 11 sources. PAH luminosities are used to determine the starburst fraction of bolometric luminosity, and model predictions for a dusty torus are used to determine the AGN fraction of luminosity in all sources based on νLν(5.5 μm). Approximately half of the sources have luminosity dominated by an AGN and approximately half by a starburst. The ratio of infrared to radio flux, defined as q = log [ fν(25 μ m)/fν(1.4 GHz) ] , does not distinguish between AGNs and starbursts for these sources.

COMPARING ULTRAVIOLET- AND INFRARED-SELECTED STARBURST GALAXIES IN DUST OBSCURATION AND LUMINOSITY

We present samples of starburst galaxies that represent the extremes discovered with infrared and ultraviolet observations, including 25 Markarian galaxies, 23 ultraviolet-luminous galaxies discovered with GALEX, and the 50 starburst galaxies having the largest infrared/ultraviolet ratios. These sources have z 2 are insufficient, and should be at least a factor of 10 for M(UV) ~ –17, with decreasing correction for more luminous sources.

Neon and [CII] 158 micron Emission Line Profiles in Dusty Starbursts and Active Galactic Nuclei

A sample of 379 extragalactic sources is presented that has mid-infrared, high-resolution spectroscopy from the Spitzer Infrared Spectrograph (IRS) and also spectroscopy of the [C II] 158 μm line from the Herschel Photodetector Array Camera and Spectrometer (PACS). The emission line profiles of [Ne II] 12.81 μm, [Ne III] 15.55 μm, and [C II] 158 μm are presented, and intrinsic line widths are determined (full width half maximum of Gaussian profiles after instrumental correction). All line profiles, together with overlays comparing the positions of PACS and IRS observations, are made available in the Cornell Atlas of Spitzer IRS Sources. Sources are classified from active galactic nucleus (AGN) to starburst based on equivalent widths of the 6.2 μm polycyclic aromatic hydrocarbon feature. It is found that intrinsic line widths do not change among classifications for [C II], with median widths of 207 km s-1 for AGNs, 248 km s-1 for composites, and 233 km s-1 for starbursts. The [Ne II] line widths also do not change with classification, but [Ne III] lines are progressively broader from starburst to AGN. A few objects with unusually broad lines or unusual redshift differences in any feature are identified.

DUSTY QUASARS AT HIGH REDSHIFTS

A population of quasars at z ~ 2 is determined based on dust luminosities vLv(7.8 um) that includes unobscured, partially obscured, and obscured quasars. Quasars are classified by the ratio vLv(0.25 um)/vLv(7.8 um) = UV/IR, assumed to measure obscuration of UV luminosity by the dust which produces IR luminosity. Quasar counts at rest frame 7.8 um are determined for quasars in the Bootes field of the NOAO Deep Wide Field Survey using 24 um sources with optical redshifts from the AGN and Galaxy Evolution Survey (AGES) or infrared redshifts from the Spitzer Infrared Spectrograph. Spectral energy distributions are extended to far infrared wavelengths using observations from the Herschel Space Observatory Spectral and Photometric Imaging Receiver (SPIRE), and new SPIRE photometry is presented for 77 high redshift quasars from the Sloan Digital Sky Survey. It is found that unobscured and obscured quasars have similar space densities at rest frame 7.8 um, but the ratio Lv(100 um)/Lv(7.8 um) is about three times higher for obscured quasars compared to unobscured, so that far infrared or submm discoveries are dominated by obscured quasars. Quasar source counts for these samples are determined for comparison to the number of submm sources that have been discovered with the SCUBA-2 camera at z ~ 2 using the Lv(100 um)/Lv(7.8 um) results together with the Bootes 7.8 um counts, and we find that only ~ 5% of high redshift submm sources are quasars, including even the most obscured quasars. Illustrative source counts are predicted to z = 10, and we show that existing SCUBA-2 850 um surveys or 2 mm surveys with the Goddard-IRAM Superconducting 2 Millimeter Observer (GISMO) survey camera should already have detected sources at z ~ 10 if quasar and starburst luminosity functions remain the same from z = 2 until z = 10.