We report the discovery of a powerful molecular wind from the nucleus of the non-interacting nearby S0 field galaxy NGC 1266. The single-dish CO profile exhibits emission to ?400 km s--1 and requires ...a nested Gaussian fit to be properly described. Interferometric observations reveal a massive, centrally concentrated molecular component with a mass of 1.1 X 109 M and a molecular outflow with a molecular mass of 2.4 X 107 M . The molecular gas close to the systemic velocity consists of a rotating, compact nucleus with a mass of about 4.1 X 108 M within a radius of 60 pc. This compact molecular nucleus has a surface density of 2.7 X 104 M pc--2, more than two orders of magnitude larger than that of giant molecular clouds in the disk of the Milky Way, and it appears to sit on the Kennicutt-Schmidt relation despite its extreme kinematics and energetic activity. We interpret this nucleus as a disk that confines the outflowing wind. A mass outflow rate of 13 M yr--1 leads to a depletion timescale of 85 Myr. The star formation in NGC 1266 is insufficient to drive the outflow, and thus it is likely driven by the active galactic nucleus. The concentration of the majority of the molecular gas in the central 100 pc requires an extraordinary loss of angular momentum, but no obvious companion or interacting galaxy is present to enable the transfer. NGC 1266 is the first known outflowing molecular system that does not show any evidence of a recent interaction.
Young radio AGN are pivotal for our understanding of many of the still-debated aspects of AGN feedback. In this paper we present a study of the interstellar medium (ISM) in the compact, ...peaked-spectrum radio galaxy PKS B1934-63 using X-shooter observations. Most of the warm ionized gas resides within a circum-nuclear disk with a radius of about 200 pc that is likely to constitute the gas reservoir from which the central black hole feeds. On the other hand, we find a biconical outflow of warm ionized gas with an estimated radius of 59 ± 12 pc. This matches the radial extent of the radio source and suggests that the outflow is jet driven. Thanks to the superior wavelength coverage of the data, we can estimate the density of the warm ionized gas using the trans-auroral line technique, and we find that the outflowing gas has remarkably high density, up to log ne (cm−3) ≃ 5.5. The estimated mass outflow rate is low (Ṁ = 10−3 −10−1 M⊙ yr−1), and the AGN feedback operates at relatively low efficiency (Ė/Lbol ∼ 10−4−10−3%). In addition, optical and near-IR line ratios show that the expansion of the radio source drives fast shocks (with velocities vs ≳ 500 km s−1) that ionize and accelerate the outflowing gas. At odds with the properties of other compact, peaked-spectrum radio sources hosting warm ionized gas outflows, we do not find signs of kinematically disturbed or outflowing gas in phases colder than the warm ionized gas. We argue that this is due to the young age of our source and thus to the recent nature of the AGN-ISM interaction, and suggest that cold gas forms within the outflowing material and the shock-ionized outflowing gas of PKS B1934-63 did not have enough time to cool down and accumulate in a colder phase. This scenario is also supported by the multi-phase outflows of other compact and young radio sources in the literature.
We present the H I emission project within the MIGHTEE survey, currently being carried out with the newly commissioned MeerKAT radio telescope. This is one of the first deep, blind, medium-wide ...interferometric surveys for neutral hydrogen (H I ) ever undertaken, extending our knowledge of H I emission to z = 0.6. The science goals of this medium-deep, medium-wide survey are extensive, including the evolution of the neutral gas content of galaxies over the past 5 billion years. Simulations predict nearly 3000 galaxies over 0 < z < 0.4 will be detected directly in H I , with statistical detections extending to z = 0.6. The survey allows us to explore H I as a function of galaxy environment, with massive groups and galaxy clusters within the survey volume. Additionally, the area is large enough to contain as many as 50 local galaxies with H I mass < 10 8 M ⊙ , which allows us to study the low-mass galaxy population. The 20 deg 2 main survey area is centred on fields with exceptional multi-wavelength ancillary data, with photometry ranging from optical through far-infrared wavelengths, supplemented with multiple spectroscopic campaigns. We describe here the survey design and the key science goals. We also show first results from the Early Science observations, including kinematic modelling of individual sources, along with the redshift, H I , and stellar mass ranges of the sample to date.
The HI absorption “Zoo” Geréb, K.; Maccagni, F. M.; Morganti, R. ...
Astronomy & astrophysics,
03/2015, Volume:
575
Journal Article
Peer reviewed
Open access
We present an analysis of the H I 21 cm absorption in a sample of 101 flux-selected radio AGN (S1.4 GHz> 50 mJy) observed with the Westerbork Synthesis Radio Telescope (WSRT). We detect H I ...absorption in 32 objects (30% of the sample). In a previous paper, we performed a spectral stacking analysis on the radio sources, while here we characterize the absorption spectra of the individual detections using the recently presented busy function. The H I absorption spectra show a broad variety of widths, shapes, and kinematical properties. The full width half maximum (FWHM) of the busy function fits of the detected H I lines lies in the range 32 km s-1<FWHM< 570 km s-1, whereas the full width at 20% of the peak absorption (FW20) lies in the range 63 km s-1<FW20< 825 km s-1. The width and asymmetry of the profiles allows us to identify three groups: narrow lines (FWHM< 100 km s-1), intermediate widths (100 km s-1<FWHM< 200 km s-1), and broad profiles (FWHM> 200 km s-1). We study the kinematical and radio source properties of each group, with the goal of identifying different morphological structures of H I. Narrow lines mostly lie at the systemic velocity and are likely produced by regularly rotating H I disks or gas clouds. More H I disks can be present among galaxies with lines of intermediate widths; however, the H I in these sources is more unsettled. We study the asymmetry parameter and blueshift/redshift distribution of the lines as a function of their width. We find a trend for which narrow profiles are also symmetric, while broad lines are the most asymmetric. Among the broadest lines, more lines appear blueshifted than redshifted, similarly to what was found by previous studies. Interestingly, symmetric broad lines are absent from the sample. We argue that if a profile is broad, it is also asymmetric and shifted relative to the systemic velocity because it is tracing unsettled H I gas. In particular, besides three of the broadest (up to FW20 = 825 km s-1) detections, which are associated with gas-rich mergers, we find three new cases of profiles with blueshifted broad wings (with FW20 ≳ 500 km s-1) in high radio power AGN. These detections are good candidates for being HI outflows. Together with the known cases of outflows already included in the sample (3C 293 and 3C 305), the detection rate of H I outflows is 5% in the total radio AGN sample. Because of the effects of spin temperature and covering factor of the outflowing gas, this fraction could represent a lower limit. However, if the relatively low detection rate is confirmed by more detailed observations, it would suggest that, if outflows are a characteristic phenomenon of all radio AGN, they would have a short depletion timescale compared to the lifetime of the radio source. This would be consistent with results found for some of the outflows traced by molecular gas. Using stacking techniques, in our previous paper we showed that compact radio sources have higher τ, FWHM, and column density than extended sources. In addition, here we find that blueshifted and broad/asymmetric lines are more often present among compact sources. In good agreement with the results of stacking, this suggests that unsettled gas is responsible for the larger stacked FWHM detected in compact sources. Therefore in such sources the H I is more likely to be unsettled. This may arise as a result of jet-cloud interactions, as young radio sources clear their way through the rich ambient gaseous medium.
We present the results of deep Westerbork Synthesis Radio Telescope observations of neutral hydrogen in 12 nearby elliptical and lenticular galaxies. The selected objects come from a representative ...sample of nearby galaxies earlier studied at optical wavelengths with the integral-field spectrograph SAURON (Spectrographic Areal Unit for Research on Optical Nebulae). They are field galaxies, or (in two cases) located in poor group environments. We detect H i– both in regular discs as well as in clouds and tails offset from the host galaxy – in 70 per cent of the galaxies. This detection rate is much higher than in previous, shallower single-dish surveys, and is similar to that for the ionized gas. The results suggest that at faint detection levels the presence of H i is a relatively common characteristic of field early-type galaxies, confirming what was suggested twenty years ago by Jura based on IRAS observations. The observed total H i masses range between a few times 106 to just over 109 M⊙. The presence of regular disc-like structures is a situation as common as H i in offset clouds and tails around early-type galaxies. All galaxies where H i is detected also contain ionized gas, whereas no H i is found around galaxies without ionized gas. Galaxies with regular H i discs tend to have strong emission from ionized gas. In these cases, the similar kinematics of the neutral hydrogen and ionized gas suggest that they form one structure. The kinematical axis of the stellar component is nearly always misaligned with respect to that of the gas. We do not find a clear trend between the presence of H i and the global age of the stellar population or the global dynamical characteristics of the galaxies. More specifically, H i detections are uniformly spread through the (V/σ, ε) diagram. If fast and slow rotators – galaxies with high and low specific angular momentum – represent the relics of different formation paths, this does not appear in the presence and characteristics of the H i. Our observations support the idea that gas accretion is common and does not happen exclusively in peculiar early-type galaxies. The links observed between the large-scale gas and the characteristics on the nuclear scale (e.g. the presence of kinematically decoupled cores, radio continuum emission etc.) suggest that for the majority of the cases the gas is acquired through merging, but the lack of correlation with the stellar population age suggests that smooth, cold accretion could be an alternative scenario, at least in some galaxies. In either case, the data suggest that early-type galaxies continue to build their mass up to the present.
Fast outflows of gas, driven by the interaction between the radio jets and interstellar medium (ISM) of the host galaxy, are being observed in an increasing number of galaxies. One such example is ...the nearby radio galaxy 3C 293. In this paper we present integral field unit observations taken with OASIS on the William Herschel Telescope, enabling us to map the spatial extent of the ionized gas outflows across the central regions of the galaxy. The jet-driven outflow in 3C 293 is detected along the inner radio lobes with a mass outflow rate ranging from ~0.05 to 0.17 M... yr... (in ionized gas) and corresponding kinetic power of ~0.5-3.5 x 1040 erg s... Investigating the kinematics of the gas surrounding the radio jets (i.e. not directly associated with the outflow), we find linewidths broader than 300 km s... up to 5 kpc in the radial direction from the nucleus (corresponding to 3.5 kpc in the direction perpendicular to the radio axis at maximum extent). Along the axis of the radio jet linewidths >400 km s... are detected out to 7 kpc from the nucleus and linewidths of >500 km s... at a distance of 12 kpc from the nucleus, indicating that the disturbed kinematics clearly extend well beyond the high surface brightness radio structures of the jets. This is suggestive of the cocoon structure seen in simulations of jet-ISM interaction and implies that the radio jets are capable of disturbing the gas throughout the central regions of the host galaxy in all directions. (ProQuest: ... denotes formulae/symbols omitted.)
We present new ATCA 21-cm line observations of the neutral hydrogen in the nearby radio galaxy Centaurus A. We image in detail (with a resolution down to 7$^{\prime\prime}$, ~100 pc) the distribution ...of H i along the dust lane. Our data have better velocity resolution and better sensitivity than previous observations. The H i extends for a total of ~15 kpc. The data, combined with a titled-ring model of the disk, allow to conclude that the kinematics of the H i is that of a regularly rotating, highly warped structure down to the nuclear scale. The parameters (in particular the inclination) of our model are somewhat different from some of the previously proposed models but consistent with what was recently derived from stellar light in a central ring. The model nicely describes also the morphology of the dust lane as observed with Spitzer. There are no indications that large-scale anomalies in the kinematics exist that could be related to supplying material for the AGN. Large-scale radial motions do exist, but these are only present at larger radii (r > 6 kpc). This unsettled gas is mainly part of a tail/arm like structure. The relatively regular kinematics of the gas in this structure suggests that it is in the process of settling down into the main disk. The presence of this structure further supports the merger/interaction origin of the H i in Cen A. From the structure and kinematics we estimate a timescale of 1.6–3.2 × 108 yr since the merging event. No bar structure is needed to describe the kinematics of the H i. The comparison of the timescale derived from the large-scale H i structure and those of the radio structure together with the relative regularity of the H i down to the sub-kpc regions does not suggest a one-to-one correspondence between the merger and the phase of radio activity. Interestingly, the radial motions of the outer regions are such that the projected velocities are redshifted compared to the regular orbits. This means that the blueshifted absorption discovered earlier and discussed in our previous paper cannot be caused by out-moving gas at large radius projected onto the centre. Therefore, the interpretation of the blueshifted absorption, together with at least a fraction of the redshifted nuclear absorption, as evidence for a regular inner disk, still holds. Finally, we also report the discovery of two unresolved clouds detected at 5.2 and 11 kpc away (in projection) from the H i disk. They are likely an other example of a left-over of the merger that brought the H i gas.
The substantial decrease in star formation density from z = 1 to the present day is curious given the relatively constant neutral gas density over the same epoch. Future radio astronomy facilities, ...including the Square Kilometre Array (SKA) and pathfinder telescopes, will provide pioneering measures of both the gas content of galaxies and star formation activity over cosmological time-scales. Here we investigate the commensalities between neutral atomic gas (H i) and radio continuum observations, as well as the complementarity of the data products. We start with the proposed H i and continuum surveys to be undertaken with the SKA precursor telescope MeerKAT, and building on this, explore optimal combinations of survey area coverage and depth of proposed H i and continuum surveys to be undertaken with the SKA1-MID instrument. Intelligent adjustment of these observational parameters results in a tiered strategy that minimizes observation time while maximizing the value of the data set, both for H i and continuum science goals. We also find great complementarity between the H i and continuum data sets, with the spectral line H i data providing redshift measurements for gas-rich, star-forming galaxies with stellar masses M
* ∼ 109 M⊙ to z ∼ 0.3, a factor of 3 lower in stellar mass than would be feasible to reach with large optical spectroscopic campaigns.
WALLABY – an SKA Pathfinder H i survey Koribalski, Bärbel S.; Staveley-Smith, L.; Westmeier, T. ...
Astrophysics and space science,
07/2020, Volume:
365, Issue:
7
Journal Article
Peer reviewed
The Widefield ASKAP L-band Legacy All-sky Blind surveY (
wallaby
) is a next-generation survey of neutral hydrogen (H
i
) in the Local Universe. It uses the widefield, high-resolution capability of ...the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of
36
×
12
-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia.
wallaby
aims to survey three-quarters of the sky (
−
90
∘
<
δ
<
+
30
∘
) to a redshift of
z
≲
0.26
, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam
−1
per 4 km s
−1
channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five,
wallaby
is expected to detect around half a million galaxies with a mean redshift of
z
∼
0.05
(∼200 Mpc). The scientific goals of
wallaby
include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H
i
properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H
i
surveys. Combined with existing and new multi-wavelength sky surveys,
wallaby
will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the
wallaby
pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).
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