Understanding the 8 micron vs. Pa-alpha relationship on sub-arcsecond scales in Luminous Infrared Galaxies

This work explores in detail the relation between the 8 micron and the Pa-alpha emissions for 122 HII regions identified in a sample of 10 low-z LIRGs with nearly constant metallicity (12 + log (O/H) ~ 8.8). We use Gemini/T-ReCS high-spatial resolution (<~ 0.4" ~ 120 pc for the average distance of 60 Mpc of our sample) mid-infrared imaging (at 8.7 micron or 10.3 micron) together with HST/NICMOS continuum and Pa-alpha images. The LIRG HII regions extend the L_8micron vs. L_Pa-alpha relation found for HII knots in the high-metallicity SINGS galaxies by about two orders of magnitude to higher luminosities. Since the metallicity of the LIRG sample is nearly constant, we can rule out this effect as a cause for the scatter seen in the relationship. In turn, it is attributed to two effects: age and PAH features. The L_8micron/L_Pa-alpha ratio, which varies by a factor of ten for the LIRG HII regions, is reproduced by a model with instantaneous star formation and ages ranging from ~ 4 to 7.5 Myr. The remaining dispersion around the model predictions for a given age is probably due to differential contributions of the PAH features (the 8.6 micron, in our case) to the 8 micron emission from galaxy to galaxy.Comment: 16 pages, 9 figures, accepted for publication in ApJ; paper with full-resolution figures can be found at: http://damir.iem.csic.es/extragalactic

Eddington-Limited Accretion in z~2 WISE-selected Hot, Dust-Obscured Galaxies

Hot, Dust-Obscured Galaxies, or "Hot DOGs", are a rare, dusty, hyperluminous galaxy population discovered by the WISE mission. Predominantly at redshifts 2-3, they include the most luminous known galaxies in the universe. Their high luminosities likely come from accretion onto highly obscured super massive black holes (SMBHs). We have conducted a pilot survey to measure the SMBH masses of five z~2 Hot DOGs via broad H_alpha emission lines, using Keck/MOSFIRE and Gemini/FLAMINGOS-2. We detect broad H_alpha emission in all five Hot DOGs. We find substantial corresponding SMBH masses for these Hot DOGs (~ 10^{9} M_sun), and their derived Eddington ratios are close to unity. These z~2 Hot DOGs are the most luminous AGNs at given BH masses, suggesting they are accreting at the maximum rates for their BHs. A similar property is found for known z~6 quasars. Our results are consistent with scenarios in which Hot DOGs represent a transitional, high-accretion phase between obscured and unobscured quasars. Hot DOGs may mark a special evolutionary stage before the red quasar and optical quasar phases, and they may be present at other cosmic epochs.Comment: 15 pages, 9 figures. Accepted by Ap

Local Luminous Infrared Galaxies. I. Spatially resolved observations with Spitzer/IRS

We present results from the Spitzer/IRS spectral mapping observations of 15 local luminous infrared galaxies (LIRGs). In this paper we investigate the spatial variations of the mid-IR emission which includes: fine structure lines, molecular hydrogen lines, polycyclic aromatic features (PAHs), continuum emission and the 9.7um silicate feature. We also compare the nuclear and integrated spectra. We find that the star formation takes place in extended regions (several kpc) as probed by the PAH emission as well as the [NeII] and [NeIII] emissions. The behavior of the integrated PAH emission and 9.7um silicate feature is similar to that of local starburst galaxies. We also find that the minima of the [NeIII]/[NeII] ratio tends to be located at the nuclei and its value is lower than that of HII regions in our LIRGs and nearby galaxies. It is likely that increased densities in the nuclei of LIRGs are responsible for the smaller nuclear [NeIII]/[NeII] ratios. This includes the possibility that some of the most massive stars in the nuclei are still embedded in ultracompact HII regions. In a large fraction of our sample the 11.3um PAH emission appears more extended than the dust 5.5um continuum emission. We find a dependency of the 11.3um PAH/7.7 um PAH and [NeII]/11.3um PAH ratios with the age of the stellar populations. Smaller and larger ratios respectively indicate recent star formation. The estimated warm (300 K < T < 1000 K) molecular hydrogen masses are of the order of 10^8 M_Sun, which are similar to those found in ULIRGs, local starbursts and Seyfert galaxies. Finally we find that the [NeII] velocity fields for most of the LIRGs in our sample are compatible with a rotating disk at ~kpc scales, and they are in a good agreement with H-alpha velocity fields.Comment: Comments: 52 pages, accepted for publicacion in ApJ

Understanding the 8 micron vs. Pa-alpha relationship on sub-arcsecond scales in Luminous Infrared Galaxies

This work explores in detail the relation between the 8 micron and the Pa-alpha emissions for 122 HII regions identified in a sample of 10 low-z LIRGs with nearly constant metallicity (12 + log (O/H) ~ 8.8). We use Gemini/T-ReCS high-spatial resolution (<~ 0.4" ~ 120 pc for the average distance of 60 Mpc of our sample) mid-infrared imaging (at 8.7 micron or 10.3 micron) together with HST/NICMOS continuum and Pa-alpha images. The LIRG HII regions extend the L_8micron vs. L_Pa-alpha relation found for HII knots in the high-metallicity SINGS galaxies by about two orders of magnitude to higher luminosities. Since the metallicity of the LIRG sample is nearly constant, we can rule out this effect as a cause for the scatter seen in the relationship. In turn, it is attributed to two effects: age and PAH features. The L_8micron/L_Pa-alpha ratio, which varies by a factor of ten for the LIRG HII regions, is reproduced by a model with instantaneous star formation and ages ranging from ~ 4 to 7.5 Myr. The remaining dispersion around the model predictions for a given age is probably due to differential contributions of the PAH features (the 8.6 micron, in our case) to the 8 micron emission from galaxy to galaxy.Comment: 16 pages, 9 figures, accepted for publication in ApJ; paper with full-resolution figures can be found at: http://damir.iem.csic.es/extragalactic

Jography: Exploring meanings, experiences and spatialities of recreational road-running

Jogging is a relatively under-researched mobile practice with much existing literature focusing on ‘serious’ and competitive running. In this paper, we provide an account of some of the movements, meanings and experiences that together help produce the practice of jogging in the south-western English city of Plymouth. Drawing upon participant diaries and interviews, we uncover rich detail about how joggers ascribe not one but a number of meanings to their practice. Some of these are positive, some are negative; some complement each other and some compete with each other. We also consider how the experiences of joggers can be shaped by their ongoing need to develop tactics capable of enabling them to negotiate space with non-joggers. This is in some contrast to more competitive running that occurs in the separated space of an athletics track. Our sense is that better awareness of the meanings and experiences of jogging will be of value if the advertised health and sustainability benefits of the practice are to be more effectively encouraged and promoted

High spatial resolution T-ReCS mid-infrared imaging of Luminous Infrared Galaxies

We present diffraction-limited (FWHM ~ 0.3arcsec) Gemini/T-ReCS mid-infrared (MIR: N-band or narrow-band at 8.7micron) imaging of four Luminous Infrared Galaxies (LIRGs) drawn from a representative local sample. The MIR emission in the central few kpc is strikingly similar to that traced by Pa-alpha, and generally consists of bright nuclear emission and several compact circumnuclear and/or extranuclear HII regions. The central MIR emission is dominated by these powerful HII regions, consistent with the majority of AGN in this local sample of LIRGs contributing a minor part of the MIR emission. The luminous circumnuclear HII regions detected in LIRGs follow the extrapolation of the 8micron vs. Pa-alpha relation found for M51 HII knots. The integrated central 3-7kpc of galaxies, however, present elevated 8micron/Pa-alpha ratios with respect to individual HII regions, similar to the integrated values for star-forming galaxies. Our results show that the diffuse 8micron emission, not directly related to the ionizing stellar population, can be as luminous as that from the resolved HII regions. Therefore, calibrations of the star formation rate for distant galaxies should be based on the integrated 8micron emission of nearby galaxies, not that of the HII regions alone.Comment: Accepted for publication in Astrophysical Journal Letters. Paper with high resolution Fig.1 can be found at http://damir.iem.csic.es/extragalactic/publications/publications.htm

Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES

We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to 8000 M_ ⊙ yr⁻¹, with a median of 150 M_ ⊙ yr⁻¹. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 M_ ⊙ yr⁻¹, with a median of 50 M_ ⊙ yr⁻¹. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order 10⁸⁻¹⁰ M_ ⊙, assuming the present-day M_(BH)-σ_★ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution

Fast Outflows in Hot Dust-obscured Galaxies Detected with Keck/NIRES

We present rest-frame optical spectroscopic observations of 24 Hot Dust-Obscured Galaxies (Hot DOGs) at redshifts 1.7–4.6 with KECK/NIRES. Our targets are selected, based on their extreme red colors, to be the highest-luminosity sources from the WISE infrared survey. In 20 sources with well-detected emission, we fit the key [O iii], Hβ, Hα, [N ii], and [S ii] diagnostic lines to constrain physical conditions. Of the 17 targets with a clear detection of the [O iii]λ5007 Å emission line, 15 display broad blueshifted and asymmetric line profiles, with widths ranging from 1000 to 8000 km s⁻¹ and blueshifts up to 3000 km s⁻¹. These kinematics provide strong evidence for the presence of massive ionized outflows of up to 8000 M_ ⊙ yr⁻¹, with a median of 150 M_ ⊙ yr⁻¹. As many as eight sources show optical emission line ratios consistent with vigorous star formation. Balmer-line star formation rates, uncorrected for reddening, range from 30 to 1300 M_ ⊙ yr⁻¹, with a median of 50 M_ ⊙ yr⁻¹. Estimates of the SFR from Spectral Energy Distribution fitting of mid- and far-infrared photometry suggest significantly higher values. We estimate the central black hole masses to be of order 10⁸⁻¹⁰ M_ ⊙, assuming the present-day M_(BH)-σ_★ relation. The bolometric luminosities and the estimated masses of the central black holes of these galaxies suggest that many of the active galactic nucleus-dominated Hot DOGs are accreting at or above their Eddington limit. The combination of ongoing star formation, massive outflows, and high Eddington ratios suggest Hot DOGs are a transitional phase in galaxy evolution