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

Evolution of the Most Luminous Dusty Galaxies

A summary of mid-infrared continuum luminosities arising from dust is given for very luminous galaxies, Lir > 10^12 solar luminosities, with 0.005 < z < 3.2 containing active galactic nuclei (AGN), including 115 obscured AGN and 60 unobscured (type 1) AGN. All sources have been observed with the Spitzer Infrared Spectrograph. Obscured AGN are defined as having optical depth > 0.7 in the 9.7 um silicate absorption feature and unobscured AGN show silicate in emission. Luminosity vLv(8 um) is found to scale as (1+z)^2.6 to z = 2.8, and luminosities vLv(8 um) are approximately 3 times greater for the most luminous unobscured AGN. Total infrared luminosities for the most luminous obscured AGN, Lir(AGN_obscured) in solar luminosities, scale as log Lir(AGN_obscured) = 12.3+-0.25 + 2.6(+-0.3)log(1+z), and for the most luminous unobscured AGN, scale as log Lir(AGN1) = 12.6+-0.15 + 2.6(+-0.3)log(1+z), indicating that the most luminous AGN are about 10 times more luminous than the most luminous starbursts. Results are consistent with obscured and unobscured AGN having the same total luminosities with differences arising only from orientation, such that the obscured AGN are observed through very dusty clouds which extinct about 50% of the intrinsic luminosity at 8 um. Both obscured and unobscured AGN should be detected to z ~ 6 by Spitzer surveys with fv(24 um) > 0.3 mJy, even without luminosity evolution for z > 2.5. By contrast, the most luminous starbursts cannot be detected for z > 3, even if luminosity evolution continues beyond z = 2.5.Comment: Includes corrected Figure 3, as publishe

Mid-Infrared Spectroscopy of Optically Faint Extragalactic 70 micron Sources

We present mid-infrared spectra of sixteen optically faint sources with 70 micron fluxes in the range 19-38mJy. The sample spans a redshift range of 0.35<z<1.9, with most lying between 0.8<z<1.6, and has infrared luminosities of 10^{12} - 10^{13} solar luminosities. Ten of 16 objects show prominent polycyclic aromatic hydrocarbon (PAH) emission features; four of 16 show weak PAHs and strong silicate absorption, and two objects have no discernable spectral features. Compared to samples with 24 micron fluxes >10mJy, the 70\um sample has steeper IR continua and higher luminosities. The PAH dominated sources are among the brightest starbursts seen at any redshift, and reside in a redshift range where other selection methods turn up relatively few sources. The absorbed sources are at higher redshifts and have higher luminosities than the PAH dominated sources, and may show weaker luminosity evolution. We conclude that a 70 micron selection extending to ~20mJy, in combination with selections at mid-IR and far-IR wavelengths, is necessary to obtain a complete picture of the evolution of IR-luminous galaxies over 0<z<2.Comment: ApJ accepte

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

Mary\u27s Fertility As The Model Of The Ascetical Life In Ephrem The Syrian\u27s Hymns Of The Nativity

My thesis is that Ephrem uses Mary\u27s pregnancy in his Hymns on the Nativity both as a model for the ascetical life and as a way of explaining, theologically, what it means to be a Christian ascetic. For Ephrem, Mary is the first to have her body transformed through the union of Christ and humanity, a transformation that prefigures both the resurrected body and the common Christian experience of Christ prior to that. Thus, the fact that Mary was physically pregnant is theologically significant for Ephrem. Mary\u27s personal and free response to God\u27s invitation uniquely illustrates that the transformative experience of God is at once spiritual and bodily; Ephrem believes that Christ provides the means for this transformation, but throughout the Hymns on the Nativity Mary\u27s pregnancy shows how to say yes to Christ in order to receive that transformation. For Ephrem, this image of the woman, in her fertility of mind and body, represents the Christian who himself would be transformed. Mary\u27s pregnancy serves to provoke our imagination to visualize Christian salvation in a very real and common way, in the image of a pregnant, expectant woman. After Mary, everyone can conceive; Mary\u27s fertility best captures the totality of the Christian experience A central aspect of my thesis is that we can best examine Ephrem\u27s development of Mary as exemplar by locating his treatment of Mary within the context of Jewish and Jewish-Christian treatments of Eve. I will argue that in this Jewish Christian Eve tradition, the problem of Eve is her deception, but even more important to Ephrem is that this tradition suggests that Eve\u27s deception resulted in the loss of humanity\u27s glory. It is both this deception and the resulting loss of glory that Ephrem believes Mary\u27s pregnancy overcomes. Ephrem\u27s description of Mary\u27s pregnancy in the Hymns of Nativity, especially his emphasis on how that pregnancy restores glory to humankind, recalls the Jewish-Christian Eve traditions

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