Optical Identifications and Studies of Infrared Sources

 

Description: Description: Description: IRAS      Description: Description: Description: SST

 

Projects: Optical Identification and Study of IRAS PSC and SST Sources, Spectroscopic Study of BIG and BIS Objects, Search and Study of Obscured IR Galaxies and ULIRGs

Years:     1995-

Team:     A.M. Mickaelian, L.A. Sargsyan, K.S. Gigoyan, L.R. Hovhannisyan, S.A. Hakopian, S.K. Balayan; D.W. Weedman, J.R. Houck, D. Barry; P. Véron, M.P. Véron-Cetty, A. Gonçalves; E. Massaro, R. Nesci, C. Rossi; A.N. Burenkov, S.N. Dodonov, V.L. Afanasiev, A.V. Moiseev

Collaborations: USA, France, Italy, Russia

Facilities: IRAS, SST, FBS low-dispersion plates, DSS1/DSS2, DFBS, BAO 2.6m, SAO 6m, and OHP 1.93m telescopes, ESO-MIDAS, software SMART, Asiago and Loiano telescopes

Publications in 2000-2011: 34

Presentations in 2005-2011: 33

Grants:   ANSEF-2001: A.M. Mickaelian (PI), Study of Starburst/AGN/Interaction Phenomena in IRAS Galaxies

              ANSEF-2011: L.A. Sargsyan (PI), Dust obscuration and velocity distribution in narrow line regions of AGN

PICS travel grants, NSF/NASA travel grants

 

 

Study of Extragalactic Infrared Sources

A.M. Mickaelian, D.W. Weedman, J.R. Houck, L.A. Sargsyan

 

1.1 The Infrared Astronomical Satellite (IRAS, http://irsa.ipac.caltech.edu/IRASdocs/iras.html) was launched on January 25, 1983. During its ten months of operation, IRAS scanned more than 96 % of the sky for 4 times at four infrared bands centered at 12, 25, 60 and 100 μm. IRAS detected about 500.000 infrared sources (included in two catalogs; IRAS Faint Source Catalog (FSC) and IRAS Point Source catalog (PSC)). So far, a big amount of this sources still are not identified in optics. Since 1995 by A. Mickaelian in Byurakan Astrophysical Observatory (BAO, , http://www.bao.am/) a project of optical identifications of IRAS point sources have been started, using the low resolution spectra of FBS plates, DSS2 images and IRAS fluxes. During last years the Digitized First Byurakan Survey (DFBS) plates have been used. The list of almost 536 identified objects (10 lists) already are published. Simultaneously to the identifications, for classifications of identified infrared sources, observations on 6-m telescope (CAO, Russia, http://w0.sao.ru/), 1.93-m telescope (OHP, France, http://www.obs-hp.fr/welcome.shtml) and 2.6-m telescope (BAO, Armenia) were obtained (about 230 sources, included in 5 published papers).

 

1.2. As part of efforts to determine the nature of faint infrared sources, hundreds of spectra have been obtained with the Infrared Spectrograph on Spitzer (IRS, http://www.spitzer.caltech.edu) of optically faint sources discovered at 24 μm with surveys using the Multiband Imaging Photometer (MIPS). The most important result is that these faint sources having fν (24 μm) ~ 1 mJy are generally at high redshift, typically z ~ 2. Most show the 9.7 μm silicate absorption feature, but some have PAH emission features and some have only a continuum with no detectable features. These results imply that the sources are optically faint because they are both distant and obscured by dust. The absorbed sources and the featureless, power-law sources have been interpreted as obscured AGN. This interpretation implies that the surface density of optically obscured AGN at high redshifts exceeds that for classical, optically discoverable AGN by a factor of two to three in infrared surveys to fν (24 μm) 1 mJy. Extremely luminous starbursts have also been found at z ~ 2 which appear similar to local starbursts in all characteristics except luminosity. To understand these high redshift, dusty sources and to interpret the Spitzer-discovered sources within scenarios for evolution in the universe, it is essential to understand how the sources of luminosity are distributed between AGN and starbursts among the overall population of sources. This requires comparison with closer, brighter examples for which AGN and starburst diagnostics within the IRS spectra can be compared to information from other wavelengths. So far, the comparison samples which show the most similar spectral shapes are the ULIRGS, but the ULIRGs have lower luminosities and smaller redshifts than the sources at z ~ 2. The ULIRGs observed with the IRS were chosen primarily on the basis of 60 μm fluxes from the IRAS and were not selected based on optical characteristics. By A.M. Mickaleian (Byurakan Astrophysical Observatory, Armenia), D.Weedman (Astronomy Department, Cornell University, Ithaca, NY), J.R. Houck (Astronomy Department, Cornell University, Ithaca, NY) and L.A. Sargsyan (Byurakan Astrophysical Observatory, Armenia), as a part of the study of infrared galaxies, a sample of extragalactic sources from the IRAS FSC which 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 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 flux on 25 μm determined with the IRS is fainter than the sensitivity limit for the FSC. Sources have 0.12 < z < 1.0 and luminosities (in ergs s-1) between 43.3 and 46.7 on 5.5 μm, encompassing the range from local ULIRGs to the most luminous sources discovered by Spitzer at z ~ 2. Median properties of the sample having silicate absorption are very similar to the ULIRG Markarian 231 in silicate strength and continuum luminosity (Figure 1).

 

PAH luminosities are used to determine the starburst luminosity within each source, and predictions from dusty torus models are used to determine the AGN luminosity. Sources have similar bolometric luminosities arising from starbursts and from AGN and are equally divided between sources dominated by starbursts and sources dominated by AGN (Figure 2).

 

The ratio of infrared to radio flux is not a measure of whether sources are dominated in the infrared by starburst or AGN luminosity (Figure 3).

 

Figure 1. Comparison of Markarian 231 (top) with average of the 19 FSC galaxies with measured silicate absorption (bottom), arbitrarily normalized.

Figure 2. Comparison of bolometric luminosities from AGN with those from starbursts for FSC sample in Table 3, assuming that log[Lir(SB)] = log[L(6.2 μm)]+ 2.7 for PAH luminosity L(6.2) and that log[Lir(AGN)] = log[L (5.5 μm)] + 0.33 for continuum luminosity L (5.5 μm). Filled squares are starbursts with PAH detections so the L(AGN) derived from continuum luminosities are upper limits for L(AGN) because some continuum may arise from the starburst; open squares are sources without PAH detections so the L(SB) derived from PAH luminosities are upper limits for L(SB) determined from upper limits on L(6.2). The star indicates Markarian 231.

 

Figure 3. Comparison of luminosities and radio strength for FSC sources; q = log[f(25 μm)/f (1.4 GHz)] in observed frame. Filled squares are starburst sources (as defined by PAH detections), and open squares are AGN (no PAH detections). The star indicates Markarian 231. Uncertainties in q are typically ± 10%, shown by the representative error bar, arising primarily from uncertainty whether to adopt ”peak” flux or ”integrated” flux for the FIRST sources.

 

 

Infrared Galactic Sources (stars with infrared excess)

L.R. Hovhannisyan , D.W. Weedman , A.M. Mickaelian, E. Le Floc’h, J.R. Houck, B.T. Soifer, K. Brand, A. Dey, B.T. Jannuzi

 

The sensitivity and efficiency of the Spitzer Space Telescope (SST, http://www.spitzer.caltech.edu) has enabled numerous wide-area surveys to seek objects which are unusually bright in the mid infrared when observed at 24 μm with the Multiband Imaging Photometer for Spitzer (MIPS). At high Galactic latitudes, these surveys include the NOAO Deep Wide Field Survey (NDWFS, http://www.noao.edu/noao/noaodeep/) in Bootes, the Spitzer Wide-area Infrared Extragalactic Survey (SWIRE, http://www.ipac.caltech.edu/SWIRE/), and the Spitzer First Look Survey (FLS, http://ssc.spitzer.caltech.edu/fls/). To date, these surveys have been used only to locate unusual extragalactic sources, primarily dusty star forming galaxies and active galactic nuclei of very high luminosity. These surveys also include numerous bright, Galactic stars. It is known from targeted observations with Spitzer that some stars have mid-infrared excesses at 24 μm, usually attributed to circumstellar dust arising in debris disks. By using similar criteria for defining infrared excess as in these previous targeted studies, it is possible to use the wide-area Spitzer surveys to produce unbiased lists of stars with infrared excesses. The high latitude surveys are especially useful, because they minimize confusion with other Galactic stars and are in regions chosen to have low zodiacal background. By L. Hovhannisyan (Byurakan Astrophysical Observatory, Armenia), D. Weedman (Astronomy Department, Cornell University, Ithaca, NY), A. Mickaelian (Byurakan Astrophysical Observatory, Armenia), E. Le Floc’h (Steward Observatory, University of Arizona, Tucson, AZ), J.R. Houck (Astronomy Department, Cornell University, Ithaca, NY), B.T. Soifer (Spitzer Science Center, California Institute of Technology, Pasadena, CA and Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA ), K. Brand (Space Telescope Science Institute, San Martin Dr., Baltimore, MD), A. Dey (National Optical Astronomy Observatory, Tucson, AZ) and B.T. Jannuzi (National Optical Astronomy Observatory, Tucson, AZ) were identified Galactic stars in the Bootes (128 sources) and FLS (140 sources) survey areas (the first two surveys for which was an access to complete and reliable catalogs), giving in total a flux limited sample of Galactic stars within an area of ~ 14 deg2 with r < 17 and fν (24μm) > 1 mJy. Among these stars, were identified those which have excess fν (24μm) compared to that expected from a stellar photosphere. In the combined sample of 268 stars, 26 stars have excesses with (K-[24]) > 0.2 mag (K is 2MASS K magnitude). One star is a known variable; the remaining 25 stars have 0.2 < (K-[24]) < 0.7 and are candidates for having debris disks. Using limits on absolute magnitude derived from proper motions, at least 12 of the stars with excesses are main sequence stars, and estimates derived from the distribution of apparent magnitudes indicate that 22 are main sequence stars. These estimates lead to the conclusion that between 5% and 10% of the main sequence field stars in these samples have infrared excesses (For main sequence stars, such excesses are attributed primarily to debris disks). This result is statistically similar to those from previous Spitzer targeted observations of much brighter, main sequence field stars.

 

Further observations of the individual stars are needed, therefore, to determine other possible sources of the identified excesses. This study primarily demonstrates the utility of combining Spitzer surveys at 24 μm with 2MASS data for bright stars to accumulate a meaningful sample of Galactic stars with apparent 24 μm excesses. Such a statistical sample is essential to eventual understanding of debris disks associated with solar-like stars and to discover other explanations of mid-infrared excess luminosity, because only a small number of targeted stars were observed with Spitzer to measure 24 μm excesses. We are planning to observe these sources by 2.6m telescope of Byurakan Astrophysical Observatory and Far Infrared Space Telescope (First, or Herschel, http://herschel.jpl.nasa.gov/).

 

Figure 1. Upper panel: color-color diagram for all Bootes sources identifying sources with (K-[24]) > 0.2 mag.; second panel: same diagram for all FLS sources; third panel: same diagram for all field stars in Bryden et al. (Bryden, G. et al. 2006, ApJ, 636, 1098.); bottom panel: same diagram for all stars with 24μm excesses in Meyer et al. (2008). Magnitude at 24 μm is defined as [24], with zero magnitude of the MIPS 24 μm fluxes corresponding to 7300 mJy. Stars with 24μm luminosity arising only from the stellar photosphere should have (K-[24]) = 0.

Figure 2. Distribution of V magnitude compared to V -K color for Bootes stars. Open circles identify objects with infrared excess in Figure 1. Range of color arises from range of spectral types included; A0 has V - K = 1, and M0 has V - K = 4.5.

 

Figure 3. Distribution of V magnitude compared to V -K color for FLS stars. Open circles identify objects with infrared excess in Figure 1. Range of color arises from range of spectral types included; A0 has V - K = 1, and M0 has V - K = 4.5.