As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze Galaxy Evolution Explorer UV, Southeastern Association ...for Research in Astronomy optical, and Spitzer IR images of the interacting galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the interaction. We investigate the multiwavelength properties of several individual star-forming complexes (clumps). Using optical and UV colors, EW(Ha), and population synthesis models we constrain the ages of the clumps and find that the median clump age is ~9 Myr. The clumps have masses ranging from a few X106 to 109 M. In general, the clumps in the tidal features have ages similar to those in the spiral region, but are less massive. The clumps provide 33%, 36%, and 70% of the far-UV, 8.0 mm, and 24 mm emission, respectively. The 8 and 24 mm luminosities are used to estimate the far-IR luminosities and the star formation rates of the clumps. The total clump star formation rate is ~2.0 ± 0.8 M yr-1, while the entire Arp 82 system is forming stars at a rate of ~4.9 ± 2.0 M yr-1. We find, for the first time, stars in the H I arc to the southeast of the NGC 2535 disk. Population synthesis models indicate that all of the observed populations have young to intermediate ages. We conclude that, although the gas disks and some old stars may have formed early on, the progenitors may have been of late-type or low surface brightness, and the evolution of these galaxies seems to have halted until the recent encounter.
Molecular gas in super spiral galaxies Lisenfeld, Ute; Ogle, Patrick M.; Appleton, Philip N. ...
Astronomy and astrophysics (Berlin),
05/2023, Letnik:
673
Journal Article
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Odprti dostop
At the highest stellar masses (log(
M
*
) ≳ 11.5
M
⊙
), only a small fraction of galaxies are disk-like and actively star-forming objects. These so-called ‘super spirals’ are ideal objects to better ...understand how galaxy evolution proceeds and to extend our knowledge about the relation between stars and gas to a higher stellar mass regime. We present new CO(1–0) data for a sample of 46 super spirals and for 18 slightly lower-mass (log(
M
*
) > 11.0
M
⊙
) galaxies with broad HI lines – HI fast-rotators (HI-FRs). We analyze their molecular gas mass, derived from CO(1–0), in relation to their star formation rate (SFR) and stellar mass, and compare the results to values and scaling relations derived from lower-mass galaxies. We confirm that super spirals follow the same star-forming main sequence (SFMS) as lower-mass galaxies. We find that they possess abundant molecular gas (mean redshift-corrected molecular gas mass fraction (log(
f
mol, zcorr
) = −1.36 ± 0.02), which lies above the extrapolation of the scaling relation with stellar mass derived from lower-mass galaxies, but within the relation between
f
mol
and the distance to the SFMS. The molecular gas depletion time,
τ
dep
=
M
mol
/SFR, is higher than for lower-mass galaxies on the SFMS (
τ
dep
= 9.30 ± 0.03, compared to
τ
dep
= 9.00 ± 0.02 for the comparison sample) and seems to continue an increasing trend with stellar mass. HI-FR galaxies have an atomic-to-molecular gas mass ratio that is in agreement with that of lower-mass galaxies, indicating that the conversion from the atomic to molecular gas proceeds in a similar way. We conclude that the availability of molecular gas is a crucial factor to enable star formation to continue and that, if gas is present, quenching is not a necessary destiny for high-mass galaxies. The difference in gas depletion time suggests that the properties of the molecular gas at high stellar masses are less favorable for star formation.
Infrared-Faint Radio Sources represent a new and unexpected class of object which is bright at radio wavelengths but unusually faint at infrared wavelengths. If, like most mJy radio sources, they ...were either conventional active or star-forming galaxies in the local Universe, we would expect them to be detectable at infrared wavelengths, and so their non-detection by the Spitzer Space Telescope is surprising. Here, we report the detection of one of these sources using very long baseline interferometry, from which we conclude that the sources are driven by active galactic nuclei. We suggest that these sources are either normal radio-loud quasars at high redshift or abnormally obscured radio galaxies.
Abstract
We present Atacama Large Millimeter/submillimeter Array observations at a spatial resolution of 0.″2 (60 pc) of CO emission from the Taffy galaxies (UGC 12914/5). The observations are ...compared with narrowband Pa
α
, mid-IR, radio continuum and X-ray imaging, plus optical spectroscopy. The galaxies have undergone a recent head-on collision, creating a massive gaseous bridge that is known to be highly turbulent. The bridge contains a complex web of narrow molecular filaments and clumps. The majority of the filaments are devoid of star formation, and fall significantly below the Kennicutt–Schmidt relationship for normal galaxies, especially for the numerous regions undetected in Pa
α
emission. Within the loosely connected filaments and clumps of gas we find regions of high velocity dispersion that appear gravitationally unbound for a wide range of likely values of
X
CO
. Like the “Firecracker” region in the Antennae system, they would require extremely high external dynamical or thermal pressure to stop them dissipating rapidly on short crossing timescales of 2–5 Myr. We suggest that the clouds may be transient structures within a highly turbulent multiphase medium that is strongly suppressing star formation. Despite the overall turbulence in the system, stars seem to have formed in compact hotspots within a kiloparsec-sized extragalactic H
ii
region, where the molecular gas has a lower velocity dispersion than elsewhere, and shows evidence for a collision with an ionized gas cloud. Like the shocked gas in the Stephan’s Quintet group, the conditions in the Taffy bridge shows how difficult it is to form stars within a turbulent, multiphase, gas.
We present a detailed analysis of the gas conditions in the H2 luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation rate (SFR ~ 0.07 $M_{\odot}$ yr-1) in spite of a gas surface ...density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~10–50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H2 line emission is factors 10–100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 326 N in the optical suggests an outflow with a terminal velocity of ~–1800 km s-1 and a mass outflow rate of 30–40 $M_{\odot}$ yr-1, which cannot be explained by star formation. The mechanical power implied by the wind, of order 1043 erg s-1, is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times are of order 107-8 yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H2 luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥1011 $M_{\odot}$ could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback.
We present 5-38 km mid-infrared spectra at a spectral resolution of R - 65-130 of a large sample of 22 starburst nuclei taken with the Infrared Spectrograph (IRS) on board the Spitzer Space ...Telescope. The spectra show a vast range of starburst SEDs. The silicate absorption ranges from essentially no absorption to heavily obscured systems with an optical depth of t sub(9.8) k sub(m) 6 5. The spectral slopes can be used to discriminate between starburst and AGN powered sources. The monochromatic continuum fluxes at 15 and 30 km enable a remarkably accurate estimate of the total infrared luminosity of the starburst. We find that the PAH equivalent width is independent of the total starburst luminosity L sub(IR) as both continuum and PAH feature scale proportionally. However, the luminosity of the 6.2 km feature scales with L sub(IR) and can be used to approximate the total infrared luminosity of the starburst. Although our starburst sample covers about a factor of 10 difference in the Ne III/Ne II ratio, we found no systematic correlation between the radiation field hardness and the PAH equivalent width or the 7.7 km/11.3 km PAH ratio. These results are based on spatially integrated diagnostics over an entire starburst region, and local variations may be "averaged out." It is presumably due to this effect that unresolved starburst nuclei with significantly different global properties appear spectrally as rather similar members of one class of objects.
We have observed warm molecular hydrogen in two nearby edge-on disk galaxies, NGC 4565 and NGC 5907, using the Spitzer high-resolution infrared spectrograph. The 0-0 S(0) 28.2 Delta *mm and 0-0 S(1) ...17.0 Delta *mm pure rotational lines were detected out to 10 kpc from the center of each galaxy on both sides of the major axis, and in NGC 4565 the S(0) line was detected at r = 15 kpc on one side. This location is beyond the transition zone where diffuse neutral atomic hydrogen starts to dominate over cold molecular gas and marks a transition from a disk dominated by high surface-brightness far-infrared (far-IR) emission to that of a more quiescent disk. It also lies beyond a steep drop in the radio continuum emission from cosmic rays (CRs) in the disk. Despite indications that star formation activity decreases with radius, the H2 excitation temperature and the ratio of the H2 line and the far-IR luminosity surface densities, Delta *S(L )/ Delta *S(L TIR), change very little as a function of radius, even into the diffuse outer region of the disk of NGC 4565. This suggests that the source of excitation of the H2 operates over a large range of radii and is broadly independent of the strength and relative location of UV emission from young stars. Although excitation in photodissociation regions is the most common explanation for the widespread H2 emission, CR heating or shocks cannot be ruled out. At r = 15 kpc in NGC 4565, outside the main UV- and radio-continuum-dominated disk, we derived a higher than normal H2 to 7.7 Delta *mm polycyclic aromatic hydrocarbon (PAH) emission ratio, but this is likely due to a transition from mainly ionized PAH molecules in the inner disk to mainly neutral PAH molecules in the outer disk. The inferred mass surface densities of warm molecular hydrogen in both edge-on galaxies differ substantially, being 4(-60) M pc--2 and 3(-50) M pc--2 at r = 10 kpc for NGC 4565 and NGC 5907, respectively. The higher values represent very unlikely point-source upper limits. The point-source case is not supported by the observed emission distribution in the spectral slits. These mass surface densities cannot support the observed rotation velocities in excess of 200 km s--1. Therefore, warm molecular hydrogen cannot account for dark matter in these disk galaxies, contrary to what was implied by a previous Infrared Space Observatory study of the nearby edge-on galaxy NGC 891.
Context. The Ge:Ga detectors used in the PACS spectrograph onboard the Herschel space telescope react to changes of the incident flux with a certain delay. This generates transient effects on the ...resulting signal which can be important and last for up to an hour. Aims. The paper presents a study of the effects of transients on the detected signal and proposes methods to mitigate them especially in the case of the unchopped mode. Methods. Since transients can arise from a variety of causes, we classified them in three main categories: transients caused by sudden variations of the continuum due to the observational mode used; transients caused by cosmic ray impacts on the detectors; transients caused by a continuous smooth variation of the continuum during a wavelength scan. We propose a method to disentangle these effects and treat them separately. In particular, we show that a linear combination of three exponential functions is needed to fit the response variation of the detectors during a transient. An algorithm to detect, fit, and correct transient effects is presented. Results. The solution proposed to correct the signal for the effects of transients substantially improves the quality of the final reduction with respect to the standard methods used for archival reduction in the cases where transient effects are most pronounced. Conclusions. The programs developed to implement the corrections are offered through two new interactive data reduction pipelines in the latest releases of the Herschel Interactive Processing Environment.
The Great Observatories All-sky LIRG Survey (GOALS) consists of a complete sample of 202 luminous infrared galaxies (LIRGs) selected from the IRAS Revised Bright Galaxy Sample (RBGS). The galaxies ...span the full range of interaction stages, from isolated galaxies to interacting pairs to late stage mergers. We present a comparison of the UV and infrared properties of 135 galaxies in GOALS observed by GALEX and Spitzer. For interacting galaxies with separations greater than the resolution of GALEX and Spitzer (~2''-6''), we assess the UV and IR properties of each galaxy individually. The contribution of the FUV to the measured star formation rate (SFR) ranges from 0.2% to 17.9%, with a median of 2.8% and a mean of 4.0% ± 0.4%. The specific star formation rate (SSFR) of the GOALS sample is extremely high, with a median value (3.9 × 10-10 yr-1) that is comparable to the highest SSFRs seen in the Spitzer Infrared Nearby Galaxies Survey sample. We examine the position of each galaxy on the IR excess-UV slope (IRX-beta) diagram as a function of galaxy properties, including IR luminosity and interaction stage. The LIRGs on average have greater IR excesses than would be expected based on their UV colors if they obeyed the same relations as starbursts with L IR < 1011 L sun or normal late-type galaxies. The ratio of L IR to the value one would estimate from the IRX-beta relation published for lower luminosity starburst galaxies ranges from 0.2 to 68, with a median value of 2.7. A minimum of 19% of the total IR luminosity in the RBGS is produced in LIRGs and ultraluminous infrared galaxies with red UV colors (beta>0). Among resolved interacting systems, 32% contain one galaxy which dominates the IR emission while the companion dominates the UV emission. Only 21% of the resolved systems contain a single galaxy which dominates both wavelengths.
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