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Register a new userThe spatial clustering of ultraluminous infrared galaxies over 1.5<z<3
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Duncan Farrah
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We present measurements of the spatial clustering of galaxies with stellar masses >10^11Msun, infrared luminosities >10^12 Lsun, and star formation rates >200Msun per year in two redshift intervals; 1.5<z<2.0 and 2<z<3. Both samples cluster very strongly, with spatial correlation lengths of r_0=14.40+/-1.99 h^-1Mpc for the 2<z<3 sample, and r_0=9.40+/-2.24 h^-1Mpc for the 1.5<z<2.0 sample. These clustering amplitudes are consistent with both populations residing in dark matter haloes with masses of ~6x10^13Msun, making them among the most biased galaxies at these epochs. We infer, from this and previous results, that a minimum dark matter halo mass is an important factor for all forms of luminous, obscured activity in galaxies at z>1, both starbursts and AGN. Adopting plausible models for the growth of DM haloes with redshift, then the haloes hosting the 2<z<3 sample will likely host the richest clusters of galaxies at z=0, whereas the haloes hosting the 1.5<z<2.0 sample will likely host poor to rich clusters at z=0. We conclude that ULIRGs at z>1 signpost stellar buildup in galaxies that will reside in clusters at z=0, with ULIRGs at increasing redshifts signposting the buildup of stars in galaxies that will reside in increasingly rich clusters.
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We present measurements of the spatial clustering of ultraluminous infrared galaxies in two redshift intervals, 1.5<z<2.0 and 2<z<3. Both samples cluster strongly, with r_0=14.40+/-1.99 h^-1 Mpc for the 2<z<3 sample, and r_0=9.40+/-2.24 h^-1 Mpc for the 1.5<z<2.0 sample, making them among the most biased galaxies at these epochs. These clustering amplitudes are consistent with both populations residing in dark matter haloes with masses of ~6x10^13 solar masses. We infer that a minimum dark matter halo mass is an important factor for all forms of luminous, obscured activity in galaxies at z>1. Adopting plausible models for the growth of DM haloes with redshift, then the haloes hosting the 2<z<3 sample will likely host the richest clusters of galaxies at z=0, whereas the haloes hosting the 1.5<z<2.0 sample will likely host poor to rich clusters at z=0.
We measure the evolution of galaxy clustering out to a redshift of z~1.5 using data from two MUSYC fields, the Extended Hubble Deep Field South (EHDF-S) and the Extended Chandra Deep Field South (ECDF-S). We use photometric redshift information to calculate the projected-angular correlation function, omega(sigma), from which we infer the projected correlation function Xi(sigma). We demonstrate that this technique delivers accurate measurements of clustering even when large redshift measurement errors affect the data. To this aim we use two mock MUSYC fields extracted from a LambdaCDM simulation populated with GALFORM semi-analytic galaxies which allow us to assess the degree of accuracy of our estimates of Xi(sigma) and to identify and correct for systematic effects in our measurements. We study the evolution of clustering for volume limited subsamples of galaxies selected using their photometric redshifts and rest-frame r-band absolute magnitudes. We find that the real-space correlation length r_0 of bright galaxies, M_r<-21 (rest-frame) can be accurately recovered out to z~1.5, particularly for ECDF-S given its near-infrared photometric coverage. There is mild evidence for a luminosity dependent clustering in both fields at the low redshift samples (up to <z>=0.57), where the correlation length is higher for brighter galaxies by up to 1Mpc/h between median rest-frame r-band absolute magnitudes of -18 to -21.5. As a result of the photometric redshift measurement, each galaxy is assigned a best-fit template; we restrict to E and E+20%Sbc types to construct subsamples of early type galaxies (ETGs). Our ETG samples show a strong increase in r_0 as the redshift increases, making it unlikely (95% level) that ETGs at median redshift z_med=1.15 are the direct progenitors of ETGs at z_med=0.37 with equivalent passively evolved luminosities. (ABRIDGED)
Ever since their discovery in the 1970s, UltraLuminous InfraRed Galaxies (ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their immense luminosities, and frustrated them due to their singularly opaque nature, almost in equal measure. Over the last decade, however, comprehensive observations from the X-ray through to the radio have produced a consensus picture of local ULIRGs, showing that they are mergers between gas rich galaxies, where the interaction triggers some combination of dust-enshrouded starburst and AGN activity, with the starburst usually dominating. Very recent results have thrown ULIRGs even further to the fore. Originally they were thought of as little more than a local oddity, but the latest IR surveys have shown that ULIRGs are vastly more numerous at high redshift, and tantalizing suggestions of physical differences between high and low redshift ULIRGs hint at differences in their formation modes and local environment. In this review we look at recent progress on understanding the physics and evolution of local ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared background and the global history of star formation, and the role of ULIRGs as diagnostics of the formation of massive galaxies and large-scale structures.
We analyze the multi-wavelength photometric and spectroscopic data of 12 ultraluminous infrared galaxies (ULIRGs) at z ~ 1 and compare them with models of stars and dust in order to study the extinction law and star formation in young infrared (IR) galaxies. Five extinction curves, namely, the Milky Way (MW), the pseudo MW which is MW-like without the 2175 Angstrom feature, the Calzetti, and two SN dust curves, are applied to the data, by combining with various dust distributions, namely, the uniform dust screen, the clumpy dust screen, the internal dust geometry, and the composite geometry with a combination of dust screen and internal dust. Employing a minimum chi square method, we find that the foreground dust screen geometry, especially combined with the 8 - 40 M_sun SN extinction curve, provides a good approximation to the real dust geometry, whereas internal dust is only significant in 2 galaxies. The SN extinction curves, which are flatter than the others, reproduce the data of 8(67%) galaxies better. Dust masses are estimated to be in excess of ~ 10^8 M_sun. Inferred ages of the galaxies are very young, 8 of which range from 10 to 650 Myr. The SN-origin dust is the most plausible to account for the vast amount of dust masses and the flat slope of the observed extinction law. The inferred dust mass per SN ranges from 0.01 to 0.4 M_sun/SN.
We present low-resolution (64 < R < 124) mid-infrared (8--38 micron) Spitzer/IRS spectra of two z~1.3 ultraluminous infrared galaxies (LFIR~10^13) discovered in a Spitzer/MIPS survey of the Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). MIPS J142824.0+352619 is a bright 160 micron source with a large infrared-to-optical flux density ratio and a possible lensing amplification of <~10. The 6.2, 7.7, 11.3, and 12.8 micron PAH emission bands in its IRS spectrum indicate a redshift of z~1.3. The large equivalent width of the 6.2 micron PAH feature indicates that at least 50% of the mid-infrared energy is generated in a starburst, an interpretation that is supported by a large [NeII]/[NeIII] ratio and a low upper limit on the X-ray luminosity. SST24 J142827.19+354127.71 has the brightest 24 micron flux (10.55 mJy) among optically faint (R > 20) galaxies in the NDWFS. Its mid-infrared spectrum lacks emission features, but the broad 9.7 micron silicate absorption band places this source at z~1.3. Given this redshift, SST24 J142827.19+354127.71 has among the largest rest-frame 5 micron luminosities known. The similarity of its SED to those of known AGN-dominated ULIRGs and its lack of either PAH features or large amounts of cool dust indicate that the powerful mid-infrared emission is dominated by an active nucleus rather than a starburst. Our results illustrate the power of the IRS in identifying massive galaxies in the ``redshift desert and in discerning their power sources. Because they are bright, MIPS J142824.0+352619 (pending future observations to constrain its lensing amplification) and SST24 J142827.19+354127.71 are useful z>1 templates of a high luminosity starburst and AGN, respectively.
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