45 research outputs found
Starburst galaxies
The infrared properties of star-forming galaxies, primarily as determined by the Infrared Astronomy Satellite (IRAS), are compared to X-ray, optical, and radio properties. Luminosity functions are reviewed and combined with those derived from optically discovered samples using 487 Markarian galaxies with redshifts and published IRAS 60 micron fluxes, and 1074 such galaxies in the Center for Astrophysics redshift survey. It is found that the majority of infrared galaxies which could be detected are low luminosity sources already known from the optical samples, but non-infrared surveys have found only a very small fraction of the highest luminosity sources. Distributions of infrared to optical fluxes and available spectra indicate that the majority of IRAS-selected galaxies are starburst galaxies. Having a census of starburst galaxies and associated dust allow severl important global calculations. The source counts are predicted as a function of flux limits for both infrared and radio fluxes. These galaxies are found to be important radio sources at faint flux limits. Taking the integrated flux to z = 3 indicates that such galaxies are a significant component of the diffuse X-ray background, and could be the the dominant component depending on the nature of the X-ray spectra and source evolution
Infrared Classification and Luminosities For Dusty AGN and the Most Luminous Quasars
Mid-infrared spectroscopic measurements from the Infrared Spectrometer on
Spitzer (IRS) are given for 125 hard X-ray AGN (14-195 keV) from the Swift
Burst Alert Telescope sample and for 32 AGN with black hole masses from
reverberation mapping. The 9.7 um silicate feature in emission or absorption
defines an infrared AGN classification describing whether AGN are observed
through dust clouds, indicating that 55% of the BAT AGN are observed through
dust. The mid-infrared dust continuum luminosity is shown to be an excellent
indicator of intrinsic AGN luminosity, scaling closely with the hard X-ray
luminosity, log vLv(7.8 um)/L(X) = -0.31 +- 0.35 and independent of
classification determined from silicate emission or absorption. Dust luminosity
scales closely with black hole mass, log vLv(7.8 um) = (37.2 +- 0.5) + 0.87 log
BHM for luminosity in erg per sec and BHM in solar masses. The 100 most
luminous type 1 quasars as measured in vLv(7.8 um) are found by comparing Sloan
Digital Sky Survey optically discovered quasars with photometry at 22 um from
the Wide-Field Infrared Survey Explorer, scaled to rest frame 7.8 um using an
empirical template determined from IRS spectra. The most luminous SDSS/WISE
quasars have the same maximum infrared luminosities for all 1.5 < z < 5,
reaching total infrared luminosity L(IR) = 10^14.4 solar luminosities.
Comparing with Dust Obscured Galaxies from Spitzer and WISE surveys, we find no
evidence of hyperluminous obscured quasars whose maximum infrared luminosities
exceed the maximum infrared luminosities of optically discovered quasars.
Bolometric luminosities L(bol) estimated from rest frame optical or ultraviolet
luminosities are compared to L(IR).Comment: accepted for publication in The Astrophysical Journa
The Most Luminous Starbursts in the Universe
A summary of starburst luminosities based on PAH features is given for 243
starburst galaxies with 0 < z < 2.5, observed with the Spitzer Infrared
Spectrograph. Luminosity vLv(7.7um) for the peak luminosity of the 7.7um PAH
emission feature is found to scale as log[vLv(7.7um)] = 44.63(+-0.09) +
2.48(+-0.28)log(1+z) for the most luminous starbursts observed. Empirical
calibrations of vLv(7.7um) are used to determine bolometric luminosity Lir and
the star formation rate (SFR) for these starbursts. The most luminous
starbursts found in this sample have log Lir = 45.4(+-0.3) +
2.5(+-0.3)log(1+z), in ergs per s, and the maximum star formation rates for
starbursts in units of solar masses per yr are log(SFR) = 2.1(+-0.3) +
2.5(+-0.3)log(1+z), up to z = 2.5. The exponent for pure luminosity evolution
agrees with optical and radio studies of starbursts but is flatter than
previous results based in infrared source counts. The maximum star formation
rates are similar to the maxima determined for submillimeter galaxies; the most
luminous individual starburst included within the sample has log Lir = 46.9,
which gives a SFR = 3400 solar masses per yr.Comment: Accepted for publication in The Astrophysical Journa
Infrared Spectra and Spectral Energy Distributions for Dusty Starbursts and AGN
We present spectroscopic results for all galaxies observed with the Spitzer
Infrared Spectrograph (IRS) which 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 um to 160 um are compared to polycyclic aromatic
hydrocarbon (PAH) emission from starburst galaxies or mid-infrared dust
continuum from AGN at rest frame wavelengths ~ 8 um. A total of 301 spectra are
analyzed for which IRS and IRAS include the same unresolved source, as measured
by the ratio fv(IRAS 25 um)/fv(IRS 25 um). Sources have 0.004 < z < 0.34 and
42.5 < log L(IR) < 46.8 (erg per s) 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)/vLv(7.7
um)] = 0.74 +- 0.18 in starbursts, that log [L(IR)/vLv(7.7 um)] = 0.96 +- 0.26
in composite sources (starburst plus AGN), that log [L(IR)/vLv(7.9 um)] = 0.80
+- 0.25 in AGN with silicate absorption, and log [L(IR)/vLv(7.9 um)] = 0.51 +-
0.21 in AGN with silicate emission. L(IR) for the most luminous absorption and
emission AGN are similar and 2.5 times larger than for the most luminous
starbursts. AGN 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.Comment: Accepted for publication in The Astrophysical Journa
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 < 0.5 and cover a luminosity range of ~ 10^4. Comparisons
between infrared luminosities determined with the 7.7 um PAH 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 solar luminosities and M(UV) the AB magnitude at rest frame 153 nm.
These results imply that obscuration corrections by factors of two to three
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)
about -17, with decreasing correction for more luminous sources.Comment: accepted for publication in The Astrophysical Journa
Average Infrared Galaxy Spectra From Spitzer Flux Limited Samples
The mid-infrared spectroscopic analysis of a flux-limited sample of galaxies
with fv(24um) > 10 mJy is presented. Sources observed are taken from the
Spitzer First Look Survey (FLS) catalog and from the NOAO Deep Wide-Field
Survey region in Bootes (NDWFS). The spectroscopic sample includes 60 of the
100 sources in these combined catalogs having fv(24um) > 10 mJy. New spectra
from the Spitzer Infrared Spectrograph are presented for 25 FLS sources and for
11 Bootes AGN; these are combined with 24 Bootes starburst galaxies previously
published to determine the distribution of mid-infrared spectral
characteristics for the total 10 mJy sample. Sources have 0.01 < z < 2.4 and
41.8 < log vLv(15um) < 46.2 (ergs/s). Average spectra are determined as a
function of luminosity; lower luminosity sources (log vLv(15um) < 44.0) are
dominated by PAH features and higher luminosity sources (log vLv(15um) > 44.0)
are dominated by silicate absorption or emission. We find that a rest frame
equivalent width of 0.4um for the 6.2um PAH emission feature provides a well
defined division between lower luminosity, "pure" starbursts and higher
luminosity AGN or composite sources. Using the average spectra, fluxes fv(24um)
which would be observed with the Spitzer MIPS are predicted as a function of
redshift for sources with luminosities that correspond to the average spectra.
AGN identical to those in this 10 mJy sample could be seen to z = 3 with
fv(24um) > 1 mJy, but starbursts fall to fv(24um) < 1 mJy by z ~ 0.5. This
indicates that substantial luminosity evolution of starbursts is required to
explain the numerous starbursts found in other IRS results having fv(24um) > 1
mJy and z ~ 2.Comment: Accepted for publication in The Astrophysical Journa
Surface Brightness of Starbursts at Low and High Redshifts
Observations in the rest frame ultraviolet from various space missions are
used to define the nearby starburst regions having the highest surface
brightness on scales of several hundred pc. The bright limit is found to be
6x10^-16 ergs/cm^2-s-A-arcsec^2 for rest frame wavelength of 1830 A. Surface
brightness in the brightest pixel is measured for 18 galaxies in the Hubble
Deep Field having z > 2.2. After correcting for cosmological dimming, we find
that the high redshift starbursts have intrinsic ultraviolet surface brightness
that is typically four times brighter than low redshift starbursts. It is not
possible to conclude whether this difference is caused by decreased dust
obscuration in the high redshift starburst regions or by intrinsically more
intense star formation. Surface brightness enhancement of starburst regions may
be the primary factor for explaining the observed increase with redshift of the
ultraviolet luminosity arising from star formation.Comment: accepted for publication in AJ; 11 pages text, 3 tables, 3 figures
(embedded