Search

Abstract We use the SPace Infrared telescope for Cosmology and Astrophysics (SPICA) project as a template to demonstrate how deep spectrophotometric surveys covering large cosmological volumes over extended fields (1– $15\, \rm{deg^2}$ ) with a mid-IR imaging spectrometer (17– $36\, \rm{\rm{\upmu m}}$ ) in conjunction with deep $70\, \rm{\rm{\upmu m}}$ photometry with a far-IR camera, at wavelengths which are not affected by dust extinction can answer the most crucial questions in current galaxy evolution studies. A SPICA-like mission will be able for the first time to provide an unobscured three-dimensional (3D, i.e. x, y, and redshift z) view of galaxy evolution back to an age of the universe of less than $\sim$ 2 Gyrs, in the mid-IR rest frame. This survey strategy will produce a full census of the Star Formation Rate (SFR) in the universe, using polycyclic aromatic hydrocarbons (PAH) bands and fine-structure ionic lines, reaching the characteristic knee of the galaxy luminosity function, where the bulk of the population is distributed, at any redshift up to $z \sim 3.5$ . Deep follow-up pointed spectroscopic observations with grating spectrometers onboard the satellite, across the full IR spectral range (17– $210\, \rm{\rm{\upmu m}}$ ), would simultaneously measure Black Hole Accretion Rate (BHAR), from high-ionisation fine-structure lines, and SFR, from PAH and low- to mid-ionisation lines in thousands of galaxies from solar to low metallicities, down to the knee of their luminosity functions. The analysis of the resulting atlas of IR spectra will reveal the physical processes at play in evolving galaxies across cosmic time, especially its heavily dust-embedded phase during the activity peak at the cosmic noon ( $z \sim 1$ –3), through IR emission lines and features that are insensitive to the dust obscuration.

Mid-infrared (mid-IR) gas-phase molecular bands are powerful diagnostics of the warm interstellar medium. We report the James Webb Space Telescope detection of the CO v = 1 − 0 (4.4 − 5.0 μm) and H2O ν2 = 1 − 0 (5.0 − 7.8 μm) ro-vibrational bands, both in absorption, toward the "s2" core in the southwest nucleus of the merging galaxy VV 114 E. All ro-vibrational CO lines up to Jlow = 33 (Elow ≈ 3000 K) are detected, as well as a forest of H2O lines up to 130, 13 (Elow ≈ 2600 K). The highest-excitation lines are blueshifted by ∼180 km s−1 relative to the extended molecular cloud, which is traced by the rotational CO (J = 3 − 2) 346 GHz line observed with the Atacama Large Millimeter/submillimeter Array. The bands also show absorption in a low-velocity component (blueshifted by ≈30 km s−1) with lower excitation. The analysis shows that the bands are observed against a continuum with an effective temperature of Tbck ∼ 550 K extinguished with τ6 μmext ∼ 2.5−3 τ 6 μ m ext ∼ 2.5 − 3 $ \tau_{{6\,{\upmu}\mathrm{m}}}^{\mathrm{ext}}\sim 2.5{-}3 $ (Ak ∼ 6.9 − 8.3 mag). The high-excitation CO and H2O lines are consistent with v = 0 thermalization with Trot ≈ 450 K and column densities of NCO ≈ (1.7 − 3.5)×1019 cm−2 and NH2O ≈ (1.5 − 3.0)×1019 cm−2. Thermalization of the v = 0 levels of H2O requires either an extreme density of nH2 ≳ 109 cm−3, or radiative excitation by the mid-IR field in a very compact (< 1 pc) optically thick source emitting ∼1010 L⊙. The latter alternative is favored, implying that the observed absorption probes the very early stages of a fully enshrouded active black hole (BH). On the basis of a simple model for BH growth and applying a lifetime constraint to the s2 core, an intermediate-mass BH (IMBH, MBH ∼ 4.5 × 104 M⊙) accreting at super-Eddington rates is suggested, where the observed feedback has not yet been able to break through the natal cocoon. [ABSTRACT FROM AUTHOR]

H2O submillimeter emission is a powerful diagnostic of the molecular interstellar medium in a variety of sources, including low- and high-mass star-forming regions of the Milky Way, and from local to high-redshift galaxies. However, the excitation mechanism of these lines in galaxies has been debated, preventing a basic consensus on the physical information that H2O provides. Radiative pumping due to H2O absorption of far-infrared photons emitted by dust and collisional excitation in dense shocked gas have both been proposed to explain the H2O emission. Here we propose two basic diagnostics to distinguish between the two mechanisms: First, the ortho-H2O 321 − 212 75 μm and the para-H2O 220 − 111 101 μm rotational lines in shock-excited regions are expected to be in emission, while when radiative pumping dominates, the two far-infrared lines are expected to be in absorption. Second, the radiative pumping scenario predicts, based on the statistical equilibrium of H2O level populations, that the apparent isotropic net rate of far-infrared absorption in the 321 ← 212 (75 μm) and 220 ← 111 (101 μm) lines should be higher than or equal to the apparent isotropic net rate of submillimeter emission in the 321 → 312 (1163 GHz) and 220 → 211 (1229 GHz) lines, respectively. Applying both criteria to all 16 galaxies and several Galactic high-mass star-forming regions in which the H2O 75 μm and submillimeter lines have been observed with Herschel/PACS and SPIRE, we show that in most (extra)galactic sources, the H2O submillimeter line excitation is dominated by far-infrared pumping, combined in some cases with collisional excitation of the lowest energy levels. Based on this finding, we revisit the interpretation of the correlation between the luminosity of the H2O 988 GHz line and the source luminosity in the combined Galactic and extragalactic sample. [ABSTRACT FROM AUTHOR]

Local luminous infrared (IR) galaxies (LIRGs) have both high star formation rates (SFR) and a high AGN (Seyfert and AGN/starburst composite) incidence. Therefore, they are ideal candidates to explore the co-evolution of black hole (BH) growth and star formation (SF) activity, not necessarily associated with major mergers. Here, we use Spitzer/IRS spectroscopy of a complete volume-limited sample of local LIRGs (distances of<78 Mpc).We estimate typical BH masses of 3 × 107M☉ using [Ne III] 15.56μm and optical [O III] λ5007 gas velocity dispersions and literature stellar velocity dispersions.We find that in a large fraction of local LIRGs, the current SFR is taking place not only in the inner nuclear ∼1.5 kpc region, as estimated from the nuclear 11.3μm PAH luminosities, but also in the host galaxy. We next use the ratios between the SFRs and BH accretion rates (BHAR) to study whether the SF activity and BH growth are contemporaneous in local LIRGs. On average, local LIRGs have SFR to BHAR ratios higher than those of optically selected Seyferts of similar active galactic nucleus (AGN) luminosities. However, the majority of the IR-bright galaxies in the revised-Shapley-Ames Seyfert sample behave like local LIRGs. Moreover, the AGN incidence tends to be higher in local LIRGs with the lowest SFRs. All of this suggests that in local LIRGs there is a distinct IR-bright star-forming phase taking place prior to the bulk of the current BH growth (i.e., AGN phase). The latter is reflected first as a composite and then as a Seyfert, and later as a non-LIRG optically identified Seyfert nucleus with moderate SF in its host galaxy. [ABSTRACT FROM AUTHOR]

ABSTRACT Numerical simulations of minor mergers, typically having mass ratios greater than 3:1, predict little enhancement in the global star formation activity. However, these models also predict that the satellite galaxy is more susceptible to the effects of the interaction than the primary. We use optical integral field spectroscopy and deep optical imaging to study the NGC 7771+NGC 7770 interacting system (∼10:1 stellar mass ratio) to test these predictions. We find that the satellite galaxy NGC 7770 is currently experiencing a galaxy-wide starburst with most of the optical light being from young and post-starburst stellar populations (<1 Gyr). This galaxy lies off the local star-forming sequence for composite galaxies with an enhanced integrated specific star formation rate. We also detect in the outskirts of NGC 7770 Hα emitting gas filaments. This gas appears to have been stripped from one of the two galaxies and is being excited by shocks. All these results are consistent with a minor-merger-induced episode(s) of star formation in NGC 7770 after the first close passage. Such effects are not observed on the primary galaxy NGC 7771. [ABSTRACT FROM AUTHOR]

We quantify the active galactic nucleus (AGN) contribution to the mid-infrared (mid-IR) and the total infrared (IR, 8-1000 µm) emission in a complete volume-limited sample of 53 local luminous infrared galaxies (LIRGs, LIR = 1011-1012 L⊙). We decompose the Spitzer Infrared Spectrograph low-resolution 5-38 µm spectra of the LIRGs into AGN and starburst components using clumpy torus models and star-forming galaxy templates, respectively. We find that 50% (25/50) of local LIRGs have an AGN component detected with this method. There is good agreement between these AGN detections through mid-IR spectral decomposition and other AGN indicators, such as the optical spectral class, mid-IR spectral features, and X-ray properties. Taking all the AGN indicators together, the AGN detection rate in the individual nuclei of LIRGs is ~62%. The derived AGN bolometric luminosities are in the range Lbol(AGN) = (0.4-50) x 1043 erg s-1. The AGN bolometric contribution to the IR luminosities of the galaxies is generally small, with 70% of LIRGs having Lbol[AGN]/LIR ≤, 0.05. Only ≃ 8% of local LIRGs have a significant AGN bolometric contribution Lbol[AGN]/LIR > 0.25. From the comparison of our results with literature results of ultraluminous infrared galaxies (LIR = 1012-1013 L⊙), we confirm that in the local universe the AGN bolometric contribution to the IR luminosity increases with the IR luminosity of the galaxy/system. If we add up the AGN bolometric luminosities we find that AGNs only account for Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed of the total IR luminosity produced by local LIRGs (with and without AGN detections). This proves that the bulk of the IR luminosity of local LIRGs is due to star formation activity. Taking the newly determined IR luminosity density of LIRGs in the local universe, we then estimate an AGN IR luminosity density of Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed in LIRGs. [ABSTRACT FROM AUTHOR]

Abstract: Luminous Infrared (IR) Galaxies (LIRGs, ) are an important cosmological class of galaxies as they are the main contributors to the co-moving star formation rate density of the universe at . In this paper we present a guaranteed time observation (GTO) Spitzer InfraRed Spectrograph (IRS) program aimed to obtain spectral mapping of a sample of 14 local LIRGs. The data cubes map, at least, the central to regions of the galaxies, and use all four IRS modules covering the full spectral range. The final goal of this project is to characterize fully the mid-IR properties of local LIRGs as a first step to understanding their more distant counterparts. In this paper we present the first results of this GTO program. The IRS spectral mapping data allow us to build spectral maps of the bright mid-IR emission lines (e.g., [Ne ii], [Ne iii], [S iii] at ), continuum, the 6.2 and polycyclic aromatic hydrocarbon (PAH) features, and the silicate feature, as well as to extract 1D spectra for regions of interest in each galaxy. The IRS data are used to obtain spatially resolved measurements of the extinction using the silicate feature, and to trace star forming regions using the neon lines and the PAH features. We also investigate a number of active galactic nuclei (AGN) indicators, including the presence of high excitation emission lines and a strong dust continuum emission at around . We finally use the integrated Spitzer/IRS spectra as templates of local LIRGs. We discuss several possible uses for these templates, including the calibration of the star formation rate of IR-bright galaxies at high redshift. We also predict the intensities of the brightest mid-IR emission lines for LIRGs as a function of redshift, and compare them with the expected sensitivities of future space IR missions. [Copyright &y& Elsevier]