The Stephan's Quintet (hereafter SQ) is a template source to study the impact of galaxies interaction on the physical state and energetics of their gas. We report on IRAM single-dish CO observations ...of the SQ compact group of galaxies. These observations follow up the Spitzer discovery of bright mid-IR H sub(2) rotational line emission (L(H sub(2)) approx = 10 super(35) W) from warm (10 super(2-3) K) molecular gas, associated with a 30 kpc long shock between a galaxy, NGC 7318b, and NGC 7319's tidal arm. We detect CO(1-0), (2-1) and (3-2) line emission in the inter-galactic medium (IGM) with complex profiles, spanning a velocity range of approx =1000 km s super(-1). The spectra exhibit the pre-shock recession velocities of the two colliding gas systems (5700 and 6700 km s super(-1)), but also intermediate velocities. This shows that much of the molecular gas has formed out of diffuse gas accelerated by the galaxy-tidal arm collision. CO emission is also detected in a bridge feature that connects the shock to the Seyfert member of the group, NGC 7319, and in the northern star forming region, SQ-A, where a new velocity component is identified at 6900 km s super(-1), in addition to the two velocity components already known. Assuming a Galactic CO(1-0) emission to H sub(2) mass conversion factor, a total H sub(2) mass of approx =5 x 10 super(9) M sub(middot in circle) is detected in the shock. The ratio between the warm H sub(2) mass derived from Spitzer spectroscopy, and the H sub(2) mass derived from CO fluxes is approx =0.3 in the IGM of SQ, which is 10--100 times higher than in star-forming galaxies. The molecular gas carries a large fraction of the gas kinetic energy involved in the collision, meaning that this energy has not been thermalized yet. The kinetic energy of the H sub(2) gas derived from CO observations is comparable to that of the warm H sub(2) gas from Spitzer spectroscopy, and a factor approx =5 greater than the thermal energy of the hot plasma heated by the collision. In the shock and bridge regions, the ratio of the PAH-to-CO surface luminosities, commonly used to measure the star formation efficiency of the H sub(2) gas, is lower (up to a factor 75) than the observed values in star-forming galaxies. We suggest that turbulence fed by the galaxy-tidal arm collision maintains a high heating rate within the H sub(2) gas. This interpretation implies that the velocity dispersion on the scale of giant molecular clouds in SQ is one order of magnitude larger than the Galactic value. The high amplitude of turbulence may explain why this gas is not forming stars efficiently.
New far-infrared and submillimeter photometry from the Herschel Space Observatory is presented for 61 nearby galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel ...(KINGFISH) sample. The spatially integrated fluxes are largely consistent with expectations based on Spitzer far-infrared photometry and extrapolations to longer wavelengths using popular dust emission models. Dwarf irregular galaxies are notable exceptions, as already noted by other authors, as their 500 mu m emission shows evidence for a submillimeter excess. In addition, the fraction of dust heating attributed to intense radiation fields associated with photodissociation regions is found to be (21 + or - 4)% larger when Herschel data are included in the analysis. Dust masses obtained from the dust emission models of Draine & Li are found to be on average nearly a factor of two higher than those based on single-temperature modified blackbodies, as single blackbody curves do not capture the full range of dust temperatures inherent to any galaxy. The discrepancy is largest for galaxies exhibiting the coolest far-infrared colors.
We present an in depth study on the evolution of galaxy properties in compact groups over the past 3 Gyr. We are using the largest multiwavelength sample to-date, comprised 1770 groups (containing ...7417 galaxies), in the redshift range of 0.01 < z < 0.23. To derive the physical properties of the galaxies, we rely on ultraviolet (UV)-to-infrared spectral energy distribution modelling, using cigale. Our results suggest that during the 3 Gyr period covered by our sample, the star formation activity of galaxies in our groups has been substantially reduced (3 to 10 times). Moreover, their star formation histories as well as their UV-optical and mid-infrared colours are significantly different from those of field and cluster galaxies, indicating that compact group galaxies spend more time transitioning through the green valley. The morphological transformation from late-type spirals to early-type galaxies occurs in the mid-infrared transition zone rather than in the UV-optical green valley. We find evidence of shocks in the emission line ratios and gas velocity dispersions of the late-type galaxies located below the star forming main sequence. Our results suggest that in addition to gas stripping, turbulence and shocks might play an important role in suppressing the star formation in compact group galaxies.
Abstract
We combine James Webb Space Telescope (JWST) and Hubble Space Telescope imaging with Atacama Large Millimeter Array CO(2–1) spectroscopy to study the highly turbulent multiphase ...intergalactic medium (IGM) in Stephan’s Quintet on 25–150 pc scales. Previous Spitzer observations revealed luminous H
2
line cooling across a 45 kpc-long filament, created by a giant shock wave, following the collision with an intruder galaxy, NGC 7318b. We demonstrate that the Mid-Infrared Instrument/F1000W/F770W filters are dominated by 0–0 S(3) H
2
and a combination of polycyclic aromatic hydrocarbon and 0–0 S(5) H
2
emission. These observations reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions, and likely destruction/recycling within different phases of the IGM. In 1 kpc-scaled structure, warm H
2
was seen to form a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H
2
. In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H
2
suggesting a cloud–cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H
2
lines throughout Stephan’s Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H
2
will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.
Abstract
We carried out deep mapping observations of the atomic hydrogen (H
i
) 21 cm line emission in a field centered on the famous galaxy group Stephan's Quintet (SQ), using the Five-hundred-meter ...Aperture Spherical Telescope (FAST) equipped with a 19-beam receiver. The final data cube reaches an H
i
column density sensitivity of 5
σ
= 2.1 × 10
17
cm
−2
per 20 km s
−1
channel with an angular resolution of 4.′0. The discovery of a large diffuse feature of the H
i
emission in the outskirts of the intragroup medium of SQ was reported in a previous paper (Xu et al.). Here we present a new study of the total H
i
emission of SQ and the detection of several neighboring galaxies, exploiting the high sensitivity and the large sky coverage of the FAST observations. A total H
i
mass of
M
H I
= 3.48 ± 0.35 × 10
10
M
☉
is found for SQ, which is significantly higher than previous measurements in the literature. This indicates that, contrary to earlier claims, SQ is not H
i
deficient. The excessive H
i
gas is mainly found in the velocity ranges of 6200–6400 km s
−1
and 6800–7000 km s
−1
, which were undetected in previous observations that are less sensitive than ours. Our results suggest that the “missing H
i
” in compact groups may be hidden in the low-density diffuse neutral gas instead of in the ionized gas.
Stephan's Quintet (SQ, co-moving radial distance = 85 ± 6 Mpc, taken from the NASA/IPAC Extragalactic Database (NED)
) is unique among compact groups of galaxies
. Observations have previously shown ...that interactions between multiple members, including a high-speed intruder galaxy currently colliding into the intragroup medium, have probably generated tidal debris in the form of multiple gaseous and stellar filaments
, the formation of tidal dwarfs
and intragroup-medium starbursts
, as well as widespread intergalactic shocked gas
. The details and timing of the interactions and collisions remain poorly understood because of their multiple nature
. Here we report atomic hydrogen (H I) observations in the vicinity of SQ with a smoothed sensitivity of 1σ = 4.2 × 10
cm
per channel (velocity bin-width Δv = 20 km s
; angular resolution = 4'), which are about two orders of magnitude deeper than previous observations
. The data show a large H I structure (with linear scale of around 0.6 Mpc) encompassing an extended source of size approximately 0.4 Mpc associated with the debris field and a curved diffuse feature of length around 0.5 Mpc attached to the south edge of the extended source. The diffuse feature was probably produced by tidal interactions in early stages of the formation of SQ (>1 Gyr ago), although it is not clear how the low-density H I gas (N
≲ 10
cm
) can survive the ionization by the intergalactic ultraviolet background on such a long time scale. Our observations require a rethinking of properties of gas in outer parts of galaxy groups and demand complex modelling of different phases of the intragroup medium in simulations of group formation.
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.
Abstract
We present Hubble Space Telescope Cosmic Origin Spectrograph (COS) UV line spectroscopy and integral-field unit (IFU) observations of the intragroup medium in Stephan’s Quintet (SQ). SQ ...hosts a 30 kpc long shocked ridge triggered by a galaxy collision at a relative velocity of 1000 km s
−1
, where large amounts of molecular gas coexist with a hot, X-ray-emitting, plasma. COS spectroscopy at five positions sampling the diverse environments of the SQ intragroup medium reveals very broad (≈2000 km s
−1
) Ly
α
line emission with complex line shapes. The Ly
α
line profiles are similar to or much broader than those of H
β
, C
ii
157.7
μ
m, and CO (1–0) emission. The extreme breadth of the Ly
α
emission, compared with H
β
, implies resonance scattering within the observed structure. Scattering indicates that the neutral gas of the intragroup medium is clumpy, with a significant surface covering factor. We observe significant variations in the Ly
α
/H
β
flux ratio between positions and velocity components. From the mean line ratio averaged over positions and velocities, we estimate the effective escape fraction of Ly
α
photons to be ≈10%–30%. Remarkably, over more than four orders of magnitude in temperature, the powers radiated by X-rays, Ly
α
, H
2
, and C
ii
are comparable within a factor of a few, assuming that the ratio of the Ly
α
to H
2
fluxes over the whole shocked intragroup medium stay in line with those observed at those five positions. Both shocks and mixing layers could contribute to the energy dissipation associated with a turbulent energy cascade. Our results may be relevant for the cooling of gas at high redshifts, where the metal content is lower than in this local system, and a high amplitude of turbulence is more common.
H2 pure-rotational emission lines are detected from warm (100-1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z < 0.22 observed with the Spitzer IR Spectrograph. The summed H2 0-0 ...S(0)-S(3) line luminosities are L(H2) = 7 X 1038-2 X 1042 erg s--1, yielding warm H2 masses up to 2 X 1010 M . These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H2 to 7.7 Delta *mm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H2)/L(PAH7.7) = 0.04-4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H2 masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H2 emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H2 in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.
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.
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