arXiv subjects

Bjorn Emonts

Publications and source records attributed to Bjorn Emonts.

48 records · Page 3Linked to original sources

arXiv2014

Outflow of hot and cold molecular gas from the obscured secondary nucleus of NGC3256: closing in on feedback physics

The nuclei of merging galaxies are often deeply buried in dense layers of gas and dust. In these regions, gas outflows driven by starburst and AGN activity are believed to play a crucial role in the evolution of these galaxies. However, to fully understand this process it is essential to resolve the morphology and kinematics of such outflows. Using near-IR integral-field spectroscopy obtained with VLT/SINFONI, we detect a kpc-scale structure of high-velocity molecular hydrogen (H2) gas associated with the deeply buried secondary nucleus of the IR-luminous merger NGC3256. We show that this structure is likely the hot component of a molecular outflow, which is detected also in the cold molecular gas by Sakamoto et al. This outflow, with a molecular gas mass of M(H2)~2x10^7 Msun, is among the first to be spatially resolved in both the hot H2 gas with VLT/SINFONI and the cold CO-emitting gas with ALMA. The hot and cold components share a similar morphology and kinematics, with a hot-to-cold molecular gas mass ratio of ~6x10^-5. The high (~100 pc) resolution at which we map the geometry and velocity structure of the hot outflow reveals a biconical morphology with opening angle ~40 deg and gas spread across a FWZI~1200 km/s. Because this collimated outflow is oriented close to the plane of the sky, the molecular gas may reach maximum intrinsic outflow velocities of ~1800 km/s, with an average mass outflow rate of at least ~20 Msun/yr. By modeling the line-ratios of various near-IR H2 transitions, we show that the H2 gas in the outflow is heated through shocks or X-rays to a temperature of ~1900K. The energy needed to drive the outflow is likely provided by a hidden Compton-thick AGN or by the nuclear starburst. We show that the global kinematics of the molecular outflow in NGC3256 mimic those of CO-outflows that have been observed at low spatial resolution in starburst- and active galaxies.

astro-ph.GA↗

arXiv2014

Star-Formation in the Ultraluminous Infrared Galaxy F00183-7111

We report the detection of molecular CO(1-0) gas in F00183-7111, one of the most extreme Ultra-Luminous Infrared Galaxies known, with the Australia Telescope Compact Array. We measure a redshift of 0.3292 for F00183-7111 from the CO(1-0) line and estimate the mass of the molecular gas in 00183 to be 1 $\times$ 10$^{10}$ M$_{\odot}$. We find that F00183-7111 is predominately powered by the AGN and only $\sim$14 per cent of the total luminosity is contributed by star-formation (SFR $\sim$220 M$_{\odot}$ yr$^{-1}$). We also present an optical image of F00183-7111, which shows an extension to the East. We searched for star-formation in this extension using radio continuum observations but do not detect any. This suggests that the star-formation is likely to be predominately nuclear. These observations provide additional support for a model in which the radio emission from ULIRGs is powered by an intense burst of star-formation and by a radio-loud AGN embedded in its nucleus, both triggered by a merger of gas-rich galaxies.

astro-ph.GA↗

arXiv2013

The location and impact of jet-driven outflows of cold gas: the case of 3C293

The nearby radio galaxy 3C293 is one of a small group of objects where extreme outflows of neutral hydrogen have been detected. However, due to the limited spatial resolution of previous observations, the exact location of the outflow was not able to be determined. In this letter, we present new higher resolution VLA observations of the central regions of this radio source and detect a fast outflow of HI with a FWZI velocity of Δv~1200 km/s associated with the inner radio jet, approximately 0.5 kpc west of the central core. We investigate possible mechanisms which could produce the observed HI outflow and conclude that it is driven by the radio-jet. However, this outflow of neutral hydrogen is located on the opposite side of the nucleus to the outflow of ionised gas previously detected in this object. We calculate a mass outflow rate in the range of 8-50 solar masses/yr corresponding to a kinetic energy power injected back into the ISM of 1.38x10^{42} - 1.00x10^{43} erg/s or 0.01 - 0.08 percent of the Eddington luminosity. This places it just outside the range required by some galaxy evolution simulations for negative feedback from the AGN to be effective in halting star-formation within the galaxy.

astro-ph.CO↗

arXiv2013

The brightest ULIRG:watching the birth of a quasar

The extreme ULIRG F00183-7111 has recently been found to have a radio-loud AGN with jets in its centre, representing an extreme example of the class of radio-loud AGNs buried within dusty star-forming galaxies. This source appears to be a rare example of a ULIRG glimpsed in the (presumably) brief period as it changes from "quasar mode" to "radio mode" activity. Such transition stages probably account for many of the high-redshift radio-galaxies and extreme high-redshift ULIRGs, and so this object at the relatively low redshift of 0.328 offers a rare opportunity to study this class of objects in detail. We have also detected the CO signal from this galaxy with the ATCA, and here describe the implications of this detection for future ULIRG studies.

astro-ph.CO↗

arXiv2012

Strong molecular hydrogen emission and kinematics of the multiphase gas in radio galaxies with fast jet-driven outflows

Observations of ionized and neutral gas outflows in radio-galaxies (RGs) suggest that AGN radio jet feedback has a galaxy-scale impact on the host ISM, but it is still unclear how the molecular gas is affected. We present deep Spitzer IRS spectroscopy of 8 RGs that show fast HI outflows. All of these HI-outflow RGs have bright H2 mid-IR lines that cannot be accounted for by UV or X-ray heating. This suggests that the radio jet, which drives the HI outflow, is also responsible for the shock-excitation of the warm H2 gas. In addition, the warm H2 gas does not share the kinematics of the ionized/neutral gas. The mid-IR ionized gas lines are systematically broader than the H2 lines, which are resolved by the IRS (with FWHM up to 900km/s) in 60% of the detected H2 lines. In 5 sources, the NeII line, and to a lesser extent the NeIII and NeV lines, exhibit blue-shifted wings (up to -900km/s with respect to the systemic velocity) that match the kinematics of the outflowing HI or ionized gas. The H2 lines do not show broad wings, except tentative detections in 3 sources. This shows that, contrary to the HI gas, the H2 gas is inefficiently coupled to the AGN jet-driven outflow of ionized gas. While the dissipation of a small fraction (<10%) of the jet kinetic power can explain the dynamical heating of the molecular gas, our data show that the bulk of the warm molecular gas is not expelled from these galaxies.

astro-ph.CO↗

arXiv2011

Classical radio source propagating into outer HI disc in NGC 3801

We present observations of a large-scale disc of neutral hydrogen (HI) in the nearby Fanaroff & Riley type-I radio galaxy NGC 3801 with the Westerbork Synthesis Radio Telescope. The HI disc (34 kpc in diameter and with M_HI = 1.3 x 10^9 M_sun) is aligned with the radio jet axis. This makes NGC 3801 an ideal system for investigating the evolution of a small radio source through its host galaxy's cold ISM. The large-scale HI disc is perpendicular to a known inner CO disc and dust-lane. We argue that the formation history of the large-scale HI disc is in agreement with earlier speculation that NGC 3801 was involved in a past gas-rich galaxy-galaxy merger (although other formation histories are discussed). The fact that NGC 3801 is located in an environment of several HI-rich companions, and shows indications of ongoing interaction with the nearby companion NGC 3802, strengthens this possibility. The large amounts of ambient cold ISM, combined with X-ray results by Croston et al (2007) on the presence of over-pressured radio jets and evidence for an obscuring torus, are properties that are generally not, or no longer, associated with more evolved FR-I radio sources. We do show, however, that the HI properties of NGC 3801 are comparable to those of a significant fraction of nearby low-power compact radio sources, suggesting that studies of NGC 3801 may reveal important insight into a more general phase in the evolution of at least a significant fraction of nearby radio galaxies.

astro-ph.CO↗

arXiv2010

Detection of molecular gas in a distant submillimetre galaxy at z=4.76 with ATCA

We have detected the CO(2-1) transition from the submillimetre galaxy (SMG) LESSJ033229.4-275619 at z=4.755 using the new Compact Array Broadband Backend system on the Australian Telescope Compact Array. These data have identified a massive gas reservoir available for star formation for the first time in an SMG at z~5. We use the luminosity and velocity width (FWHM of 160 km/s) of the CO(2--1) line emission to constrain the gas and dynamical mass of Mgas~1.6x10^10 Msun and Mdyn(<2kpc)~5x10^10 (0.25/sin^2(i)) Msun, respectively, similar to that observed for SMGs at lower redshifts of z~2-4, although we note that our observed CO FWHM is a factor of ~3 narrower than typically seen in SMGs. Together with the stellar mass we estimate a total baryonic mass of Mbary~1x10^11 Msun, consistent with the dynamical mass for this young galaxy within the uncertainties. Dynamical and baryonic mass limits of high-redshift galaxies are useful tests of galaxy formation models: using the known z~4-5 SMGs as examples of massive baryonic systems, we find that their space density is consistent with that predicted by current galaxy formation models. In addition, these observations have helped to confirm that z~4-5 SMGs possess the baryonic masses and gas consumption timescales necessary to be the progenitors of the luminous old red galaxies seen at z~3. Our results provide a preview of the science that ALMA will enable on the formation and evolution of the earliest massive galaxies in the Universe.

astro-ph.CO↗

arXiv2009

HI in radio galaxies: prospects for upcoming wide-field surveys

We present results of an ongoing systematic study of the large-scale properties of neutral hydrogen (HI) gas in nearby radio galaxies. Our main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. From an HI study of a complete sample of classical low-power radio galaxies we find that the host galaxies of extended Fanaroff & Riley type-I radio sources are generally HI poor (< 10E8 M_sun) and show no indications for gas-rich galaxy mergers or ongoing gas-rich interactions. In contrast, the host galaxies of a significant fraction of low-power compact radio sources contain enormous discs/rings of HI gas (with sizes up to 190 kpc and masses up to 2 x 10E10 M_sun). This segregation in HI mass with radio source size likely indicates that these compact radio sources are either confined by large amounts of gas in the central region, or that their fueling is inefficient and different from the fueling process of classical FR-I radio sources. To a first order, the overall HI properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short phase that occurs at some point during the lifetime of many early-type galaxies. We discuss how upcoming HI surveys (e.g. with ASKAP and Apertif) are essential for studying in a statistical way the the connection between the presence and morphology of a radio-loud AGN and the properties of the cold HI gas associated with its host galaxy.

astro-ph.CO↗

arXiv2009

Broad HI absorption in the candidate binary black-hole 4C37.11 (B2 0402+379)

We report the discovery of extremely broad 21-cm HI absorption (FWZI ~1600 km/s) detected with the Westerbork Synthesis Radio Telescope in the radio source 4C37.11 (B2 0402+379). This object has been claimed to host a super-massive binary black hole (Rodriguez et al. 2006). The main features in the absorption profile are two components, separated by ~1100 km/s. The HI absorption in 4C37.11 is unusual because it is the first case where such broad absorption is found to be centred on the systemic velocity of the host galaxy and not asymmetric and blueshifted as is seen in all other galaxies with broad HI absorption. Given the large width of the absorption, we suggest that a possible explanation for the extreme properties of the HI absorption is that it is the kinematic signature of a binary black hole. If this interpretation is correct, the combined black hole mass derived from the absorption profile is consistent with that derived from the luminosity of the spheroid. If the broad absorption is indeed due to a binary black hole, this finding confirms the importance of the gaseous component in the merging process of supermassive black holes.

astro-ph.CO↗

arXiv2008

Cold gas & mergers: fundamental difference in HI properties of different types of radio galaxies?

We present results of a study of large-scale neutral hydrogen (HI) gas in nearby radio galaxies. We find that the early-type host galaxies of different types of radio sources (compact, FR-I and FR-II) appear to contain fundamentally different large-scale HI properties: enormous regular rotating disks and rings are present around the host galaxies of a significant fraction of low power compact radio sources, while no large-scale HI is detected in low power, edge-darkened FR-I radio galaxies. Preliminary results of a study of nearby powerful, edge-brightened FR-II radio galaxies show that these systems generally contain significant amounts of large-scale HI, often distributed in tail- or bridge-like structures, indicative of a recent galaxy merger or collision. Our results suggest that different types of radio galaxies may have a different formation history, which could be related to a difference in the triggering mechanism of the radio source. If confirmed by larger studies with the next generation radio telescopes, this would be in agreement with previous optical studies that suggest that powerful FR-II radio sources are likely triggered by galaxy mergers and collisions, while the lower power FR-I sources are fed in other ways (e.g. through the accretion of hot IGM). The giant HI disks/rings associated with some compact sources could - at least in some cases - be the relics of much more advanced mergers.

astro-ph↗

arXiv2007

Fast neutral outflows in nearby radio galaxies: a major source of feedback

Fast (~1000 km/s) outflows of neutral gas (from 21-cm HI absorption) are detected in strong radio sources. The outflows occur, at least in some cases, at distances from the radio core that range between few hundred parsecs and kpc. These HI outflows likely originate from the interaction between radio jets and the dense surrounding medium. The estimated mass outflow rates are comparable to those of moderate starburst-driven superwinds. The impact on the evolution of the host galaxies is discussed.

astro-ph↗

arXiv2003

HI on large and small scales in starburst radio galaxies

The study of the optical continuum of radio galaxies shows that about 30% have a young stellar population component. Among them are the most far-IR bright radio galaxies. A further indication of the relatively gas rich environment of these galaxies (possibly related to the recent merger from which they originate) is the high fraction being detected in HI. Here we present recent results obtained from the study of neutral hydrogen (detected either in emission or absorption) in a group of starburst radio galaxies. In some objects, large-scale (tens of kpc) structures involving HI masses exceeding 10^9 M_sun are observed. In these cases, the HI can be used to study the origin and evolution of these systems and the timescales involved. In this respect, the parameters obtained from the study of the stellar populations and from the HI can be complementary. In other objects, very broad (> 1000 km/s), mostly blueshifted HI is detected in absorption. This result shows that, despite the extremely energetic phenomena occurring near an AGN - including the powerful radio jet - some of the outflowing gas remains, or becomes again, neutral. This can give new and important insights in the physical conditions of the gaseous medium around an AGN. The possible origin of the extreme kinematics is discussed.

astro-ph↗