Exploring the Connection Between Star Formation and AGN Activity in the Local Universe

We study a combined sample of 264 star-forming, 51 composite, and 73 active galaxies using optical spectra from SDSS and mid-infrared (mid-IR) spectra from the Spitzer Infrared Spectrograph. We examine optical and mid-IR spectroscopic diagnostics that probe the amount of star formation and relative energetic con- tributions from star formation and an active galactic nucleus (AGN). Overall we find good agreement between optical and mid-IR diagnostics. Misclassifications of galaxies based on the SDSS spectra are rare despite the presence of dust obscuration. The luminosity of the [NeII] 12.8 micron emission-line is well correlated with the star formation rate (SFR) measured from the SDSS spectra, and this holds for the star forming, composite, and AGN-dominated systems. AGN show a clear excess of [NeIII] 15.6 micron emission relative to star forming and composite systems. We find good qualitative agreement between various parameters that probe the relative contributions of the AGN and star formation, including: the mid-IR spectral slope, the ratio of the [NeV] 14.3 micron to [NeII] micron 12.8 fluxes, the equivalent widths of the 7.7, 11.3, and 17 micron PAH features, and the optical "D" parameter which measures the distance a source lies from the locus of star forming galaxies in the optical BPT emission-line diagnostic diagram. We also consider the behavior of the three individual PAH features by examining how their flux ratios depend upon the degree of AGN-dominance. We find that the PAH 11.3 micron feature is significantly suppressed in the most AGN-dominated systems

A Spitzer Unbiased Ultradeep Spectroscopic Survey

We carried out an unbiased, spectroscopic survey using the low-resolution module of the infrared spectrograph (IRS) on board Spitzer targeting two 2.6 square arcminute regions in the GOODS-North field. IRS was used in spectral mapping mode with 5 hours of effective integration time per pixel. One region was covered between 14 and 21 microns and the other between 20 and 35 microns. We extracted spectra for 45 sources. About 84% of the sources have reported detections by GOODS at 24 microns, with a median F_nu(24um) ~ 100 uJy. All but one source are detected in all four IRAC bands, 3.6 to 8 microns. We use a new cross-correlation technique to measure redshifts and estimate IRS spectral types; this was successful for ~60% of the spectra. Fourteen sources show significant PAH emission, four mostly SiO absorption, eight present mixed spectral signatures (low PAH and/or SiO) and two show a single line in emission. For the remaining 17, no spectral features were detected. Redshifts range from z ~ 0.2 to z ~ 2.2, with a median of 1. IR Luminosities are roughly estimated from 24 microns flux densities, and have median values of 2.2 x 10^{11} L_{\odot} and 7.5 x 10^{11} L_{\odot} at z ~ 1 and z ~ 2 respectively. This sample has fewer AGN than previous faint samples observed with IRS, which we attribute to the fainter luminosities reached here.Comment: Published in Ap

Comparison of absolute gain photometric calibration between Planck/HFI and Herschel/SPIRE at 545 and 857 GHz

We compare the absolute gain photometric calibration of the Planck/HFI and Herschel/SPIRE instruments on diffuse emission. The absolute calibration of HFI and SPIRE each relies on planet flux measurements and comparison with theoretical far-infrared emission models of planetary atmospheres. We measure the photometric cross calibration between the instruments at two overlapping bands, 545 GHz / 500 $\mu$m and 857 GHz / 350 $\mu$m. The SPIRE maps used have been processed in the Herschel Interactive Processing Environment (Version 12) and the HFI data are from the 2015 Public Data Release 2. For our study we used 15 large fields observed with SPIRE, which cover a total of about 120 deg^2. We have selected these fields carefully to provide high signal-to-noise ratio, avoid residual systematics in the SPIRE maps, and span a wide range of surface brightness. The HFI maps are bandpass-corrected to match the emission observed by the SPIRE bandpasses. The SPIRE maps are convolved to match the HFI beam and put on a common pixel grid. We measure the cross-calibration relative gain between the instruments using two methods in each field, pixel-to-pixel correlation and angular power spectrum measurements. The SPIRE / HFI relative gains are 1.047 ($\pm$ 0.0069) and 1.003 ($\pm$ 0.0080) at 545 and 857 GHz, respectively, indicating very good agreement between the instruments. These relative gains deviate from unity by much less than the uncertainty of the absolute extended emission calibration, which is about 6.4% and 9.5% for HFI and SPIRE, respectively, but the deviations are comparable to the values 1.4% and 5.5% for HFI and SPIRE if the uncertainty from models of the common calibrator can be discounted. Of the 5.5% uncertainty for SPIRE, 4% arises from the uncertainty of the effective beam solid angle, which impacts the adopted SPIRE point source to extended source unit conversion factor (Abridged)Comment: 13 pages, 10 figures; Incorporates revisions in response to referee comments; cross calibration factors unchange

Ultraluminous Star-forming Galaxies and Extremely Luminous Warm Molecular Hydrogen Emission at z = 2.16 in the PKS 1138–26 Radio Galaxy Protocluster

A deep Spitzer Infrared Spectrograph map of the PKS 1138–26 galaxy protocluster reveals ultraluminous polycyclic aromatic hydrocarbon (PAH) emission from obscured star formation in three protocluster galaxies, including Hα-emitter (HAE) 229, HAE 131, and the central Spiderweb Galaxy. Star formation rates of ~500-1100 M_☉ yr^(–1) are estimated from the 7.7 μm PAH feature. At such prodigious formation rates, the galaxy stellar masses will double in 0.6-1.1 Gyr. We are viewing the peak epoch of star formation for these protocluster galaxies. However, it appears that extinction of Hα is much greater (up to a factor of 40) in the two ULIRG HAEs compared to the Spiderweb. This may be attributed to different spatial distributions of star formation-nuclear star formation in the HAEs versus extended star formation in accreting satellite galaxies in the Spiderweb. We find extremely luminous mid-IR rotational line emission from warm molecular hydrogen in the Spiderweb Galaxy, with L(H_2 0-0 S(3)) = 1.4 × 10^(44) erg s^(–1) (3.7 × 10^(10) L_☉), ~20 times more luminous than any previously known H2 emission galaxy (MOHEG). Depending on the temperature, this corresponds to a very large mass of >9 × 10^(6)-2 × 10^9 M_☉ of T > 300 K molecular gas, which may be heated by the PKS 1138–26 radio jet, acting to quench nuclear star formation. There is >8 times more warm H_2 at these temperatures in the Spiderweb than what has been seen in low-redshift (z < 0.2) radio galaxies, indicating that the Spiderweb may have a larger reservoir of molecular gas than more evolved radio galaxies. This is the highest redshift galaxy yet in which warm molecular hydrogen has been directly detected

DustPedia: Multiwavelength photometry and imagery of 875 nearby galaxies in 42 ultraviolet-microwave bands

Aims. The DustPedia project is capitalising on the legacy of the Herschel Space Observatory, using cutting-edge modelling techniques to study dust in the 875 DustPedia galaxies – representing the vast majority of extended galaxies within 3000 km s-1 that were observed by Herschel. This work requires a database of multiwavelength imagery and photometry that greatly exceeds the scope (in terms of wavelength coverage and number of galaxies) of any previous local-Universe survey. Methods. We constructed a database containing our own custom Herschel reductions, along with standardised archival observations from GALEX, SDSS, DSS, 2MASS, WISE, Spitzer, and Planck. Using these data, we performed consistent aperture-matched photometry, which we combined with external supplementary photometry from IRAS and Planck. Results. We present our multiwavelength imagery and photometry across 42 UV-microwave bands for the 875 DustPedia galaxies. Our aperture-matched photometry, combined with the external supplementary photometry, represents a total of 21 857 photometric measurements. A typical DustPedia galaxy has multiwavelength photometry spanning 25 bands. We also present the Comprehensive & Adaptable Aperture Photometry Routine (CAAPR), the pipeline we developed to carry out our aperture-matched photometry. CAAPR is designed to produce consistent photometry for the enormous range of galaxy and observation types in our data. In particular, CAAPR is able to determine robust cross-compatible uncertainties, thanks to a novel method for reliably extrapolating the aperture noise for observations that cover a very limited amount of background. Our rich database of imagery and photometry is being made available to the community

Planck 2015 results: I. Overview of products and scientific results

The European Space Agency's Planck satellite, which is dedicated to studying the early Universe and its subsequent evolution, was launched on 14 May 2009. It scanned the microwave and submillimetre sky continuously between 12 August 2009 and 23 October 2013. In February 2015, ESA and the Planck Collaboration released the second set of cosmology products based ondata from the entire Planck mission, including both temperature and polarization, along with a set of scientific and technical papers and a web-based explanatory supplement. This paper gives an overview of the main characteristics of the data and the data products in the release, as well as the associated cosmological and astrophysical science results and papers. The data products include maps of the cosmic microwave background (CMB), the thermal Sunyaev-Zeldovich effect, diffuse foregrounds in temperature and polarization, catalogues of compact Galactic and extragalactic sources (including separate catalogues of Sunyaev-Zeldovich clusters and Galactic cold clumps), and extensive simulations of signals and noise used in assessing uncertainties and the performance of the analysis methods. The likelihood code used to assess cosmological models against the Planck data is described, along with a CMB lensing likelihood. Scientific results include cosmological parameters derived from CMB power spectra, gravitational lensing, and cluster counts, as well as constraints on inflation, non-Gaussianity, primordial magnetic fields, dark energy, and modified gravity, and new results on low-frequency Galactic foregrounds

Ultra-deep Spitzer Mid-Infrared Spectroscopy of LIRGs and ULIRGs at z ~ 1-2

We present ultra-deep mid-IR spectra of 48 infrared-luminous galaxies in the GOODS-South field obtained with the InfraRed Spectrograph (IRS) on the Spitzer Space Telescope. These galaxies are selected among faint infrared sources (0.14 - 0.5 mJy at 24 um) in two redshift bins (0.76-1.05 and 1.75-2.4) to sample the major contributors to the cosmic infrared background at the most active epochs. We estimate redshifts for 92% of the sample using PAH and Si absorption features. Only few of these galaxies (5% at z~1 and 12% at z~2) have their total infrared luminosity dominated by emission from AGN. The averaged mid-IR spectra of the z~1 LIRGs and of the z~2 ULIRGs are very similar to the averaged spectrum of local starbursts and HII-like ULIRGs, respectively. We find that 6.2um PAH equivalent widths reach a plateau of ~1 um for L(24 mu) < 1E11 L(sun). At higher luminosities, EW (6.2 mu) anti-correlates with L(24 um). Intriguingly, high-z ULIRGs and SMG lie above the local EW (6.2 um) - L(24 um) relationship suggesting that, at a given luminosity, high-z ULIRGs have AGN contributions to their dust emission lower than those of local counterparts. A quantitative analysis of their morphology shows that most of the luminous IR galaxies have morphologies similar to those of IR-quiet galaxies at the same redshift. All z~2 ULIRGs of our sample are IR-excess BzK galaxies and most of them have L(FIR)/L(1600A) ratios higher than those of starburst galaxies at a given UV slope. The ``IR excess'' (Daddi et al. 2007) is mostly due to strong 7.7 um PAH emission and under-estimation of UV dust extinction. On the basis of the AGN-powered L (6 um) continuum measured directly from the mid-IR spectra, we estimate an average intrinsic X-ray AGN luminosity of L(2-10 keV) = (0.1 +/- 0.6) 1E43 erg/s, a value substantially lower than the prediction by Daddi et al. (2007).Comment: 45 pages, 36 figures, 2 tables, accepted for publication on Ap

Candidate high-z proto-clusters among the Planck compact sources, as revealed by Herschel-SPIRE

By determining the nature of all the Planck compact sources within 808.4 deg2 of large Herschel surveys, we have identified 27 candidate proto-clusters of dusty star forming galaxies (DSFGs) that are at least 3σ overdense in either 250, 350 or 500 μm sources. We find roughly half of all the Planck compact sources are resolved by Herschel into multiple discrete objects, with the other half remaining unresolved by Herschel. We find a significant difference between versions of the Planck catalogues, with earlier releases hosting a larger fraction of candidate proto-clusters and Galactic Cirrus than later releases, which we ascribe to a difference in the filters used in the creation of the three catalogues. We find a surface density of DSFG candidate proto-clusters of (3.3 ± 0.7) × 10−2 sources deg−2, in good agreement with previous similar studies. We find that a Planck colour selection of S857/S545 1. Our candidate proto-clusters are a factor of 5 times brighter at 353 GHz than expected from simulations, even in the most conservative estimates. Further observations are needed to confirm whether these candidate proto-clusters are physical clusters, multiple proto-clusters along the line of sight, or chance alignments of unassociated sources