Searching for the Highest Redshift Sources in 250-500 μm Submillimeter Surveys

We explore a technique for identifying the highest redshift (z>4) sources in Herschel/SPIRE and BLAST submillimeter surveys by localizing the position of the far-infrared dust peak. Just as Spitzer/IRAC was used to identify stellar "bump" sources, the far-IR peak is also a redshift indicator; although the latter also depends on the average dust temperature. We demonstrate the wide range of allowable redshifts for a reasonable range of dust temperatures and show that it is impossible to constraint the redshift of individual objects using solely the position of the far-IR peak. By fitting spectral energy distribution models to simulated Herschel/SPIRE photometry we show the utility of radio and/or far-infrared data in breaking this degeneracy. With prior knowledge of the dust temperature distribution it is possible to obtain statistical samples of high redshift submillimeter galaxy (SMG) candidates. We apply this technique to the BLAST survey of ECDFS to constrain the number of dusty galaxies at z>4. We find 8 ± 2 galaxies with flux density ratios of S_(500)_>S_(350); this sets an upper limit of 17 ± 4 deg^(–2) if we assume all are at z>4. This is 45 mJy (L_(IR)>2 × 10^(13) L_☉ for z>4). Modeling with conventional temperature and redshift distributions estimates the percentage of these 500 μm peak galaxies at z>4 to be between 10% and 85%. Our results are consistent with other estimates of the number density of very high redshift SMGs and follow the decline in the star formation rate density at z>4

Early Science with the Large Millimeter Telescope: Detection of Dust Emission in Multiple Images of a Normal Galaxy at z > 4 Lensed by a Frontier Fields Cluster

We directly detect dust emission in an optically detected, multiply imaged galaxy lensed by the Frontier Fields cluster MACSJ0717.5+3745. We detect two images of the same galaxy at 1.1 mm with the AzTEC camera on the Large Millimeter Telescope leaving no ambiguity in the counterpart identification. This galaxy, MACS0717_Az9, is at z > 4 and the strong lensing model (μ = 7.5) allows us to calculate an intrinsic IR luminosity of 9.7 × 10^(10) L_⊙ and an obscured star formation rate of 14.6 ± 4.5 M_⊙ yr^(−1). The unobscured star formation rate from the UV is only 4.1 ± 0.3 M_⊙ yr^(−1), which means the total star formation rate (18.7 ± 4.5 M_⊙ yr^(−1)) is dominated (75%–80%) by the obscured component. With an intrinsic stellar mass of only 6.9 × 10^9 M_⊙, MACS0717_Az9 is one of only a handful of z > 4 galaxies at these lower masses that is detected in dust emission. This galaxy lies close to the estimated star formation sequence at this epoch. However, it does not lie on the dust obscuration relation (IRX-β) for local starburst galaxies and is instead consistent with the Small Magellanic Cloud attenuation law. This remarkable lower mass galaxy, showing signs of both low metallicity and high dust content, may challenge our picture of dust production in the early universe

Starburst or AGN Dominance in Submillimetre-Luminous Candidate AGN?

It is widely believed that ultraluminous infrared (IR) galaxies and active galactic nuclei (AGN) activity are triggered by galaxy interactions and merging, with the peak of activity occurring at z~2, where submillimetre galaxies are thousands of times more numerous than local ULIRGs. In this evolutionary picture, submillimetre galaxies (SMGs) would host an AGN, which would eventually grow a black hole (BH) strong enough to blow off all of the gas and dust leaving an optically luminous QSO. To probe this evolutionary sequence we have focussed on the 'missing link' sources, which demonstrate both strong starburst (SB) and AGN signatures, in order to determine if the SB is the main power source even in SMGs when we have evidence that an AGN is present from their IRAC colours. The best way to determine if a dominant AGN is present is to look for their signatures in the mid-infrared with the Spitzer IRS, since often even deep X-ray observations miss identifying the presence of AGN in heavily dust-obscured SMGs. We present the results of our audit of the energy balance between star-formation and AGN within this special sub-population of SMGs -- where the BH has grown appreciably to begin heating the dust emission.Comment: 2 pages, 1 figure. To appear in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista and C.C. Popescu, AIP Conf. Ser., in pres

On the Periphery: Examining Women’s Exclusion from Core Leadership Roles in the “Extremely Gendered” Organization of Men’s Club Football in England

This paper frames men’s club football as an “extremely gendered” organization to explain the underrepresentation of women leaders within the industry. By analyzing women’s leadership work over a 30-year period, we find that women’s inclusion has been confined to a limited number of occupational areas. These areas are removed, in terms of influence and proximity, from the male players and the playing of football. These findings reveal a gendered substructure within club football that maintains masculine dominance in core football facing leadership roles and relegates women to a position of peripheral inclusion in leadership roles. Through a discourse analysis of gender pay gap reports, we show that men’s football clubs legitimatize women’s peripheral inclusion by naturalizing male-dominance at the organizational core. These findings are significant as they demonstrate that men’s football clubs, as masculine conferring organizations, have excluded women from core roles in order to maintain their masculine character while superficially accepting women into roles that do not challenge the association of football with hegemonic masculinity. As such, organizational change may only be possible if women are granted greater access to core organizational roles. This paper offers a new theoretical framework for “extremely gendered” organizations that can be applied to other sporting and male-dominated contexts to analyze women’s access to core leadership roles

On the cross-correlation of sub-mm sources and optically-selected galaxies

Bright sub-mm galaxies are expected to arise in massive highly-biased haloes, and hence exhibit strong clustering. We argue that a valuable tool for measuring these clustering properties is the cross-correlation of sub-mm galaxies with faint optically-selected sources. We analyze populations of SCUBA-detected and optical galaxies in the GOODS-N survey area. Using optical/IR photometric-redshift information, we search for correlations induced by two separate effects: (1) cosmic magnification of background sub-mm sources by foreground dark matter haloes traced by optical galaxies at lower redshifts; and (2) galaxy clustering due to sub-mm and optical sources tracing the same population of haloes where their redshift distributions overlap. Regarding cosmic magnification, we find no detectable correlation. Our null result is consistent with a theoretical model for the cosmic magnification, and we show that a dramatic increase in the number of sub-mm sources will be required to measure the effect reliably. Regarding clustering, we find evidence at the 3.5-sigma level for a cross-correlation between sub-mm and optical galaxies analyzed in identical photometric redshift slices. The data hint that the sub-mm sources have an enhanced bias parameter compared to the optically-selected population (with a significance of 2-sigma). The next generation of deep sub-mm surveys can potentially perform an accurate measurement of each of these cross-correlations, adding a new set of diagnostics for understanding the development of massive structure in the Universe.Comment: 10 pages, 10 figures, accepted for publication by MNRA