Sargsyan L.,Cornell University |
Samsonyan A.,Byurakan Astrophysical Observatory |
Lebouteiller V.,Cornell University |
Lebouteiller V.,University Paris Diderot |
And 5 more authors.
Astrophysical Journal | Year: 2014
A summary is presented for 130 galaxies observed with the Herschel Photodetector Array Camera and Spectrometer instrument to measure fluxes for the [C II] 158 μm emission line. Sources cover a wide range of active galactic nucleus to starburst classifications, as derived from polycyclic aromatic hydrocarbon strength measured with the Spitzer Infrared Spectrograph. Redshifts from [C II] and line to continuum strengths (equivalent width (EW) of [C II]) are given for the full sample, which includes 18 new [C II] flux measures. Calibration of L([C II)]) as a star formation rate (SFR) indicator is determined by comparing [C II] luminosities with mid-infrared [Ne II] and [Ne III] emission line luminosities; this gives the same result as determining SFR using bolometric luminosities of reradiating dust from starbursts: log SFR = log L([C II)])-7.0, for SFR in M yr-1 and L([C II]) in L . We conclude that L([C II]) can be used to measure SFR in any source to a precision of ∼50%, even if total source luminosities are dominated by an active galactic nucleus (AGN) component. The line to continuum ratio at 158 μm, EW([C II]), is not significantly greater for starbursts (median EW([C II]) = 1.0 μm) compared to composites and AGNs (median EW([C II]) = 0.7 μm), showing that the far-infrared continuum at 158 μm scales with [C II] regardless of classification. This indicates that the continuum at 158 μm also arises primarily from the starburst component within any source, giving log SFR = log νL ν(158 μm)-42.8 for SFR in M yr-1 and νL ν(158 μm) in erg s-1. © 2014. The American Astronomical Society. All rights reserved..
Nazaryan T.A.,Byurakan Astrophysical Observatory
Astrophysics | Year: 2014
418 pairs containing galaxies from the Second Byurakan Survey (SBS) with dV < 800 km/s and Dp < 100 kpc are selected for study of the dependence of star formation rates and nuclear activity on the kinematics of the pairs and on the morphologies and masses of the paired galaxies. The following basic results are obtained: SBS galaxies with neighbors do not differ spectral type from isolated SBS galaxies. The SBS galaxies are brighter than their neighbors by 0m.5 on the average, but there is no statistically significant difference in their colors, morphologies, and star formation rates. There is a weak, but statistically significant correlation between the morphologies of the paired galaxies. The neighbors of the SBS galaxies have a lower fraction of star forming galaxies and a higher fraction of galaxies in all the other spectral types. The specific (relative) star formation rate (SSFR) is higher for galaxies that are closer to a neighboring galaxy for galaxies of all morphological types. The enhancement is the greatest for galaxies of earlier types (by 1 dex) and less for galaxies of later morphological types. There is an increase of SSFR of galaxies within all ranges of masses. Both major and minor interactions can increase the SSFR by 0.7 dex, but the effect is greater for major interactions, while in the case of minor interactions the SSFR increases only in the massive members of the pairs. The existence of neighbor galaxy of earlier morphological types does not enhance the SSFR, neighbor galaxies of the same morphological types produce a moderate increase in the SSFR, while neighboring galaxies of later morphological types cause a significant increase in the SSFR. © 2014 Springer Science+Business Media New York.
Sargsyan L.A.,Byurakan Astrophysical Observatory |
Weedman D.W.,Cornell University |
Houck J.R.,Cornell University
Astrophysical Journal | Year: 2010
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 < 0.5 and cover a luminosity range of ∼ 104. Comparisons between infrared luminosities determined with the 7.7 μm polycyclic aromatic hydrocarbon feature and ultraviolet luminosities from the stellar continuum at 153 nm are used to determine obscuration in starbursts and dependence of this obscuration on infrared or ultraviolet luminosity. A strong selection effect arises for the ultraviolet-selected samples: the brightest sources appear bright because they have the least obscuration. Obscuration correction for the ultraviolet-selected Markarian+GALEX sample has the form log[UV(intrinsic)/UV(observed)] = 0.07(±0.04)M(UV) + 2.09 ± 0.69 but for the full infrared-selected Spitzer sample is log[UV(intrinsic)/ UV(observed)] = 0.17(0.02)M(UV) + 4.55 0.4. The relation of total bolometric luminosity L ir to M(UV) is also determined for infrared-selected and ultraviolet-selected samples. For ultraviolet-selected galaxies, log L ir = -(0.33 ± 0.04)M(UV) + 4.52 ± 0.69. For the full infrared-selected sample, log L ir = -(0.23 ± 0.02)M(UV) + 6.99 ± 0.41, all for L ir in L⊙ and M(UV) the AB magnitude at rest frame 153 nm. These results imply that obscuration corrections by factors of 2-3 determined from reddening of the ultraviolet continuum for Lyman break galaxies with z>2 are insufficient, and should be at least a factor of 10 for M(UV) ∼ -17, with decreasing correction for more luminous sources. © 2010. The American Astronomical Society.
Sargsyan L.,Cornell University |
Lebouteiller V.,University Paris Diderot |
Weedman D.,Cornell University |
Spoon H.,Cornell University |
And 7 more authors.
Astrophysical Journal | Year: 2012
Results are presented for [C II] 158 μm line fluxes observed with the Herschel PACS instrument in 112 sources with both starburst and active galactic nucleus (AGN) classifications, of which 102 sources have confident detections. Results are compared with mid-infrared spectra from the Spitzer Infrared Spectrometer and with L ir from IRAS fluxes; AGN/starburst classifications are determined from equivalent width of the 6.2 μm polycyclic aromatic hydrocarbon (PAH) feature. It is found that the [C II] line flux correlates closely with the flux of the 11.3 μm PAH feature independent of AGN/starburst classification, log [f([C II] 158 μm)/f(11.3 μm PAH)] = -0.22 ± 0.25. It is concluded that the [C II] line flux measures the photodissociation region associated with starbursts in the same fashion as the PAH feature. A calibration of star formation rate (SFR) for the starburst component in any source having [C II] is derived comparing [C II] luminosity L([C II]) to L ir with the result that log SFR = log L([C II)]) - 7.08 ± 0.3, for SFR in M yr-1 and L([C II]) in L . The decreasing ratio of L([C II]) to L ir in more luminous sources (the "[C II] deficit") is shown to be a consequence of the dominant contribution to L ir arising from a luminous AGN component because the sources with the largest L ir and smallest L([C II])/L ir are AGNs. © 2012. The American Astronomical Society. All rights reserved.
Ghazaryan S.,University Paris Diderot |
Alecian G.,University Paris Diderot |
Harutyunian H.,Byurakan Astrophysical Observatory
Monthly Notices of the Royal Astronomical Society | Year: 2013
HgMn stars are affected by atomic diffusion processes. Because theoretical models based on atomic diffusion require that the atmospheres of ApBp stars have to be much more stable than those of normal stars, the detectionor the absence of detection of granulation in them should be an interestinginformation for the modelling. We would like to address the question of thestability of the atmospheres of HgMn stars by analysing the light curves provided by the Convection Rotation and planetary Transits (CoRoT) satellite.We used the CoRoT light curves of the bright HgMn star HD 175640 observed through asteroseismology channel, to look for granulation signature.We have developed a new quasi-automatic IDL procedure, which allows us to correct abnormal jumps and variations which exist in CoRoT N2 data. The earlier results show that this procedure is an appropriate tool for the analysis of data obtained through asteroseismology and exoplanet channels. Calculations wecarried out for this target show that granulation signature in this HgMn star is not detected from CoRoT light curves. On the other hand, we do not detect clear pulsation signal for this star. That shows that even if some HgMn stars are pulsating, this is not a general property of the group. © 2013 The Authors Published by Oxford University Press on behalf of the RoyalAstronomical Society.