Abstract Understanding how galaxies quench their star formation is crucial for studies of galaxy evolution. Quenching is related to a decrease of cold gas. In the first paper we showed that the dust ...removal timescale in early-type galaxies (ETGs) is about 2.5 Gyr. Here we present carbon monoxide and 21 cm hydrogen line observations of these galaxies and measure the timescale of removal of the cold interstellar medium (ISM). We find that all the cold ISM components (dust and molecular and atomic gas) decline at similar rates. This allows us to rule out a wide range of potential ISM-removal mechanisms (including starburst-driven outflows, astration, or a decline in the number of asymptotic giant branch stars), and artificial effects like the stellar mass–age correlation, environmental influence, mergers, and selection bias, leaving ionization by evolved low-mass stars and ionization/outflows by Type Ia supernovae or active galactic nuclei as viable mechanisms. We also provide evidence for an internal origin of the detected ISMs. Moreover, we find that the quenching of star formation in these galaxies cannot be explained by a reduction in the gas amount alone, because the star formation rates (SFRs) decrease faster (on a timescale of about 1.8 Gyr) than the amount of cold gas. Furthermore, the star formation efficiency (SFE) of the ETGs ( SFE ≡ SFR / M H 2 ) is lower than that of star-forming galaxies, whereas their gas mass fractions ( f H 2 ≡ M H 2 / M * ) are normal. This may be explained by the stabilization of gas against fragmentation, for example due to morphological quenching, turbulence, or magnetic fields.
GOALS: The Great Observatories All-Sky LIRG Survey Armus, L.; Mazzarella, J. M.; Evans, A. S. ...
Publications of the Astronomical Society of the Pacific,
06/2009, Letnik:
121, Številka:
880
Journal Article
Recenzirano
Odprti dostop
The Great Observatories All-Sky LIRG Survey (GOALS20) combines data from NASA’sSpitzer Space Telescope,
Chandra X-Ray Observatory,
Hubble Space Telescope(HST), andGalaxy Evolution Explorer(GALEX) ...observatories, together with ground-based data, into a comprehensive imaging and spectroscopic survey of over 200 low-redshift (
z < 0.088
z
<
0.088
), Luminous Infrared Galaxies (LIRGs). The LIRGs are a complete subset of theIRASRevised Bright Galaxy Sample (RBGS), which comprises 629 extragalactic objects with 60 μm flux densities above 5.24 Jy, and Galactic latitudes above five degrees. The LIRGs targeted in GOALS span the full range of nuclear spectral types defined via traditional optical line-ratio diagrams (type-1 and type-2 AGN, LINERs, and starbursts) as well as interaction stages (major mergers, minor mergers, and isolated galaxies). They provide an unbiased picture of the processes responsible for enhanced infrared emission in galaxies in the local Universe. As an example of the analytic power of the multiwavelength GOALS data set, we presentSpitzer, Chandra, HST,andGALEXimages and spectra for the interacting system VV 340 (IRAS
F14547 + 2449
F
14547
+
2449
). TheSpitzerMIPS imaging data indicates that between 80–95% of the total far-infrared emission (or about5 × 1011 L
⊙
5
×
10
11
L
⊙
) originates in VV 340 north. While theSpitzerIRAC colors of VV 340 north and south are consistent with star-forming galaxies, both theSpitzerIRS andChandraACIS data indicate the presence of an AGN in VV 340 north. The observed line fluxes, without correction for extinction, imply that the AGN accounts for less than 10%–20% of the observed infrared emission. The X-ray data are consistent with a heavily absorbed (
N
H
≥1024 cm-2
N
H
≥
10
24
cm
-
2
) AGN. The GALEX far and near-UV fluxes imply a extremely large infrared “excess” (IRX) for the system (FIR/Ffuv ∼ 81
F
IR
/
F
fuv
∼
81
) which is well above the correlation seen in starburst galaxies. Most of this excess is driven by VV 340 N, which has an IR excess of nearly 400. The VV 340 system seems to be comprised of two very different galaxies: an infrared luminous edge-on galaxy (VV 340 north) that dominates the long-wavelength emission from the system, which hosts a buried AGN; and a face-on starburst (VV 340 south) that dominates the short-wavelength emission.
We present the first results of a survey of the CII157.7 mu m emission line in 241 luminous infrared galaxies (LIRGs) comprising the Great Observatories All-sky LIRG Survey (GOALS) sample, obtained ...with the PACS instrument on board the Herschel Space Observatory. The CII luminosities, L sub(CII), of the LIRGs in GOALS range from ~10 super(7) to 2 x 10 super(9) L sub(middot in circle). We find that LIRGs show a tight correlation of CII/FIR with far-IR (FIR) flux density ratios, with a strong negative trend spanning from ~10 super(-2) to 10 super(-4), as the average temperature of dust increases. We find correlations between the CII/FIR ratio and the strength of the 9.7 mu m silicate absorption feature as well as with the luminosity surface density of the mid-IR emitting region (summationoperator sub(MIR)), suggesting that warmer, more compact starbursts have substantially smaller CII/FIR ratios. Pure star-forming LIRGs have a mean CII/FIR ~ 4 x 10 super(-3), while galaxies with low polycyclic aromatic hydrocarbon (PAH) equivalent widths (EWs), indicative of the presence of active galactic nuclei (AGNs), span the full range in CII/FIR. However, we show that even when only pure star-forming galaxies are considered, the CII/FIR ratio still drops by an order of magnitude, from 10 super(-2) to 10 super(-3), with summationoperator sub(MIR) and summationoperator sub(IR), implying that the CII157.7 mu m luminosity is not a good indicator of the star formation rate (SFR) for most local LIRGs, for it does not scale linearly with the warm dust emission most likely associated to the youngest stars. Moreover, even in LIRGs in which we detect an AGN in the mid-IR, the majority (2/3) of galaxies show CII/FIR > or =, slanted 10 super(-3) typical of high 6.2 mu m PAH EW sources, suggesting that most AGNs do not contribute significantly to the FIR emission. We provide an empirical relation between the CII/FIR and the specific SFR for star-forming LIRGs. Finally, we present predictions for the starburst size based on the observed CII and FIR luminosities which should be useful for comparing with results from future surveys of high-redshift galaxies with ALMA and CCAT.
Aims: We use the deepest existing mid- and far-infrared observations (reaching ~3 mJy at 70 μm) obtained with Spitzer in the Great Observatories Origins Deep Survey (GOODS) and Far Infrared Deep ...Extragalactic Legacy survey (FIDEL) fields to derive the evolution of the rest-frame 15 μm, 35 μm, and total infrared luminosity functions of galaxies spanning z<1.3. We thereby quantify the fractional contribution of infrared luminous galaxies to the comoving star formation rate density over this redshift range. In comparison with previous studies, the present one takes advantage of deep 70 μm observations that provide a more robust infrared luminosity indicator than 24 μm affected by the emission of PAHs at high redshift (z∼1), and we use several independent fields to control cosmic variance. Methods: We used a new extraction technique based on the well-determined positions of galaxies at shorter wavelengths to extract the 24 and 70 μm flux densities of galaxies. It is found that sources separated by a minimum of 0.5 × FWHM are deblended by this technique, which facilitates multi-wavelength associations of counterparts. Using a combination of photometric and spectroscopic redshifts that exist for ~80% of the sources in our sample, we are able to estimate the rest-frame luminosities of galaxies at 15 μm and 35 μm. By complementing direct detections with a careful stacking analysis, we measured the mid- and far-infrared luminosity functions of galaxies over a factor ~100 in luminosity (1011~L⊙ <∼ L_IR <∼ 1013~L⊙) at z<1.3. A stacking analysis was performed to validate the bolometric corrections and to compute comoving star-formation rate densities in three redshift bins 0.4<z<0.7, 0.7<z<1.0 and, 1.0<z<1.3. Results: We find that the average infrared spectral energy distribution of galaxies over the last 2/3 of the cosmic time is consistent with that of local galaxies, although individual sources do present significant scatter. We also measured both the bright and faint ends of the infrared luminosity functions and find no evidence for a change in the slope of the double power law used to characterize the luminosity function. The redshift evolution of infrared luminous galaxies is consistent with pure luminosity evolution proportional to (1+z)3.6±0.4 up to z∼1.3. We do not find evidence of differential evolution between LIRGs and ULIRGs up to z∼1.3, in contrast with previous claims. The comoving number density of infrared luminous galaxies has increased by a factor of ∼100 between 0<z<1. By z∼1.0, LIRGs produce half of the total comoving infrared luminosity density.
We report measurements of the carbon monoxide ground state rotational transition ( super(12)C super(16)O J = 1-0) with the Zpectrometer ultrawideband spectrometer on the 100 m diameter Green Bank ...Telescope. The sample comprises 11 galaxies with redshifts between z = 2.1 and 3.5 from a total sample of 24 targets identified by Herschel-ATLAS photometric colors from the SPIRE instrument. Nine of the CO measurements are new redshift determinations, substantially adding to the number of detections of galaxies with rest-frame peak submillimeter emission near 100 mu m. The CO detections confirm the existence of massive gas reservoirs within these luminous dusty starforming galaxies (DSFGs). The CO redshift distribution of the 350 mu m selected galaxies is strikingly similar to the optical redshifts of 850 mu -selected submillimeter galaxies in 2.1 < or =, slanted z < or = z, slanted 3.5. Spectroscopic redshifts break a temperature-redshift degeneracy; optically thin dust models fit to the far-infrared photometry indicate characteristic dust temperatures near 34 K for most of the galaxies we detect in CO. Detections of two warmer galaxies, and statistically significant nondetections, hint at warmer or molecule-poor DSFGs with redshifts that are difficult to determine from Herschel-SPIRE photometric colors alone. Many of the galaxies identified by H-ATLAS photometry are expected to be amplified by foreground gravitational lenses. Analysis of CO linewidths and luminosities provides a method for finding approximate gravitational lens magnifications mu from spectroscopic data alone, yielding mu ~ 3-20. Corrected for magnification, most galaxy luminosities are consistent with an ultraluminous infrared galaxy classification, but three are candidate hyper-LIRGs with luminosities greater than 10 super(13) L sub(middot in circle).
We report on an accounting of the star-formation- and accretion-driven energetics of 24 Delta *mm-detected sources in the Great Observatories Origins Deep Survey-North field. For sources having ...infrared (IR; 8-1000 Delta *mm) luminosities 3 X 1012 L when derived by fitting local spectral energy distributions (SEDs) to 24 Delta *mm photometry alone, we find these IR luminosity estimates to be a factor of ~4 times larger than those estimated when the SED fitting includes additional 16 and 70 Delta *mm data (and in some cases mid-IR spectroscopy and 850 Delta *mm data). This discrepancy arises from the fact that high-luminosity sources at z 0 appear to have far- to mid-IR ratios, as well as aromatic feature equivalent widths, typical of lower luminosity galaxies in the local universe. Using our improved estimates for IR luminosity and active galactic nucleus (AGN) contributions, we investigate the evolution of the IR luminosity density versus redshift arising from star formation and AGN processes alone. We find that, within the uncertainties, the total star-formation-driven IR luminosity density is constant between 1.15 z 2.35, although our results suggest a slightly larger value at z 2. AGNs appear to account for 18% of the total IR luminosity density integrated between 0 z 2.35, contributing 25% at each epoch. Luminous infrared galaxies (LIRGs; 1011 L <= L IR < 1012 L ) appear to dominate the star formation rate density along with normal star-forming galaxies (L IR < 1011 L ) between 0.6 z 1.15. Once beyond z 2, the contribution from ultraluminous infrared galaxies (L IR >= 1012 L ) becomes comparable with that of LIRGs. Using our improved IR luminosity estimates, we find existing calibrations for UV extinction corrections based on measurements of the UV spectral slope typically overcorrect UV luminosities by a factor of ~2, on average, for our sample of 24 Delta *mm-selected sources; accordingly we have derived a new UV extinction correction more appropriate for our sample.
With a 100 m × 110 m off-axis paraboloid dish, the Green Bank Telescope (GBT) is the largest fully steerable radio telescope on Earth. A major challenge facing large ground-based radio telescopes is ...achieving sufficient pointing accuracy for observing at high frequencies, up to 116 GHz in the case of the GBT. Accurate pointing requires the ability to blindly acquire source locations and perform ad hoc corrections determined by observing nearby calibrator sources in order to obtain a starting position accurate to within a small margin of error of the target’s location. The required pointing accuracy is dependent upon the half-power beamwidth, and for the higher-frequency end of GBT observing, this means that pointing must be accurate to within a few arcseconds RMS. The GBT’s off-axis design is advantageous in that it eliminates blockage of the dish and reduces sidelobe interference, and there is no evidence that the resulting asymmetric structure adversely affects pointing accuracy. However, factors such as gravitational flexure, thermal deformation, azimuth track tilt and irregularity, and small misalignments and offset errors within the telescope’s structure cause pointing inaccuracies. A pointing model was developed for the GBT to correct for these effects. The model utilizes standard geometrical corrections along with metrology data from the GBT’s structural temperature sensors and data from measurements of the track levels. In this paper we provide a summary of the GBT’s pointing model and associated corrections, as well as a discussion of relevant metrology systems and an analysis of its current nighttime pointing accuracy.
ABSTRACT
We report the detection of the far-infrared (FIR) fine-structure line of singly ionized nitrogen, N ii 205 $\mu$m , within the peak epoch of galaxy assembly, from a strongly lensed galaxy, ...hereafter ‘The Red Radio Ring’; the RRR, at z = 2.55. We combine new observations of the ground-state and mid-J transitions of CO (Jup = 1, 5, 8), and the FIR spectral energy distribution (SED), to explore the multiphase interstellar medium (ISM) properties of the RRR. All line profiles suggest that the H ii regions, traced by N ii 205 $\mu$m , and the (diffuse and dense) molecular gas, traced by CO, are cospatial when averaged over kpc-sized regions. Using its mid-IR-to-millimetre (mm) SED, we derive a non-negligible dust attenuation of the N ii 205 $\mu$m line emission. Assuming a uniform dust screen approximation results a mean molecular gas column density >1024 cm−2, with a molecular gas-to-dust mass ratio of 100. It is clear that dust attenuation corrections should be accounted for when studying FIR fine-structure lines in such systems. The attenuation corrected ratio of $L_{\rm N\,{\small II}205} / L_{\rm IR(8\!-\!1000\, \mu m)} = 2.7 \times 10^{-4}$ is consistent with the dispersion of local and z > 4 SFGs. We find that the lower limit, N ii 205 $\mu$m -based star formation rate (SFR) is less than the IR-derived SFR by a factor of 4. Finally, the dust SED, CO line SED, and $L_{\rm N\,{\small II}205}$ line-to-IR luminosity ratio of the RRR is consistent with a starburst-powered ISM.
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