S. Hüttemeister

Overluminous HNC line emission in Arp 220, NGC 4418 and Mrk 231. Global IR pumping or XDRs?

Context. In recent studies of 3 mm J = 1 - 0 HNC emission from galaxies it is found that the emission is often bright which is unexpected in warm, star forming clouds. We propose that the main cause for the luminous HNC line emission is the extreme radiative and kinematical environment in starburst and active nuclei. Aims. To determine the underlying excitational and chemical causes behind the luminous HNC emission in active galaxies and to establish how HNC emission may serve to identify important properties of the nuclear source. Methods. We present mm and submm JCMT, IRAM 30 m and CSO observations of the J = 3 - 2 line of HNC and its isomer HCN in three luminous galaxies and J = 4 - 3 HNC observations of one galaxy. The observations are discussed in terms of physical conditions and excitation as well as in the context of X-ray influenced chemistry. Results. The ultraluminous mergers Arp 220 and Mrk 231 and the luminous IR galaxy NGC 4418 show the HNC J 3 - 2 emission being brighter than the HCN 3 - 2 emission by factors of 1.5 to 2. We furthermore report the detection of HNC J = 4 - 3 in Mrk 231. Overluminous HNC emission is unexpected in warm molecular gas in ultraluminous galaxies since I( HNC) greater than or similar to I( HCN) is usually taken as a signature of cold (10 - 20 K) dark clouds. Since the molecular gas of the studied galaxies is warm (T(k) greater than or similar to 40 K), we present two alternative explanations to the overluminous HNC: a) HNC excitation is affected by pumping of the rotational levels through the mid-infrared continuum and b) XDRs (X-ray Dominated Regions) influence the abundances of HNC. HNC may become pumped at 21.5 mu m brightness temperatures of T(B) greater than or similar to 50 K, suggesting that HNC-pumping could be common in warm, ultraluminous galaxies with compact IR- nuclei. This means that the HNC emission is no longer dominated by collisions and its luminosity may not be used to deduce information on gas density. On the other hand, all three galaxies are either suspected of having buried AGN - or the presence of AGN is clear (Mrk 231) - indicating that X-rays may affect the ISM chemistry. Conclusions. We conclude that both the pumping and XDR alternatives imply molecular cloud ensembles distinctly different from those of typical starforming regions in the Galaxy, or the ISM of less extreme starburst galaxies. The HNC molecule shows the potential of becoming an additional important tracer of extreme nuclear environments.

The radio structure of radio-quiet quasars

Aims.We investigate the radio emitting structures of radio-quiet active galactic nuclei with an emphasis on radio-quiet quasars to study their connection to Seyfert galaxies. Methods: .We present and analyse high-sensitivity VLA radio continuum images of 14 radio-quiet quasars and six Seyfert galaxies. Results: .Many of the low redshift radio-quiet quasars show radio structures that can be interpreted as jet-like outflows. However, the detection rate of extended radio structures on arcsecond scales among our sample decreases with increasing redshift and luminosity, most likely due to a lack of resolution. The morphologies of the detected radio emission indicate strong interactions of the jets with the surrounding medium. We also compare the radio data of seven quasars with corresponding HST images of the [O III] emitting narrow-line region (NLR). We find that the scenario of interaction between the radio jet and the NLR gas is confirmed in two sources by structures in the NLR gas distribution as previously known for Seyfert galaxies. The extended radio structures of radio-quiet quasars at sub-arcsecond resolution are by no means different from that of Seyferts. Among the luminosities studied here, the morphological features found are similar in both types of objects while the overall size of the radio structures increases with luminosity. This supports the picture where radio-quiet quasars are the scaled-up versions of Seyfert galaxies. In addition to known luminosity relations we find a correlation of the NLR size and the radio size shared by quasars and Seyferts.

Warm and Cold Molecular Gas in Galaxies

New and archival interferometric 12CO (1→0) data sets from six nearby galaxies are combined with H2 2.122 μm and Hα maps to explore in detail the interstellar medium in different star-forming galaxies. We investigate the relation between warm (H2 at T ~ 2000 K) and cold (CO at T ~ 50 K) molecular gas from 100 pc to 2 kpc scales. On these scales, the ratio of warm-to-cold molecular hydrogen correlates with the fν(60 μm)/fν(100 μm) ratio, which tracks the star formation activity level. This result also holds for the global properties of galaxies from a much larger sample drawn from the literature. The trend persists for over 3 orders of magnitude in the mass ratio, regardless of source nuclear activity.

Triggering and Feedback: The Relation between the H I Gas and the Starburst in the Dwarf Galaxy NGC 1569

As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (H I) in the starburst dwarf galaxy NGC 1569. High-resolution measurements with the Very Large Array (B, C, and D configuration) are aimed at identifying morphological and kinematical signatures in H I caused by the starburst. Our kinematical data suggest a huge hole in the H I distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale H I structure, we confirm the existence of a possible H I companion and a so-called H I bridge east of NGC 1569. Furthermore, we report the detection of additional low-intensity H I halo emission, which leads us to suggest a revised halo structure. On the basis of our new picture, we discuss the origin of the halo gas and possible implications for the evolution of the starburst in NGC 1569.

The detection of the (J, K) = (18, 18) line of NH3

The first astronomical detection of the metastable (

A search for radio supernovae and supernova remnants in the region of NGC 1569's super star clusters

J,K

NGC 5218 – a starburst driven LINER galaxy? High resolution CO, radio continuum and H i-absorption

) = (18,18) line of NH3 is reported. With 3130 K above the ground state, this is the NH3 line with by far the highest energy detected in interstellar space. It is observed in absorption toward the galactic center star forming region Sgr B2. There is a clear detection toward Sgr B2(M) and a likely one toward SgrB2(N). An upper limit for emission is determined for Orion-KL. If we combine the (18,18) line results from Sgr B2(M) with the previously measured (12,12) absorption line, we find a rotation temperature of >1300 K for the absorbing cloud. This is at least a factor of two higher than previously derived values from less highly excited ammonia lines, giving a lower limit to the kinetic temperature. There is a hot low density gas component in the envelope of SgrB2. It is possible that the (18,18) line arises in this region. The radial velocity of the low density, hot envelope is the same as that of the dense hot cores, so the (18,18) line could also arise in the dense hot cores where non-metastable (J>K) absorption lines from energy levels of up to 1350 K above the ground state have been observed. A discussion of scenarios is presented.

Sub-Arcsecond Imaging of the Radio Continuum and Neutral Hydrogen in the Medusa Merger

We have used MERLIN, at 1.4 and 5 GHz, to search for radio supernovae (RSNe) and supernova remnants (SNRs) in the unobscured irregular dwarf galaxy NGCu20091569, and in particular in the region of its super star clusters (SSCs) A and B. Throughout NGCu20091569 we find some 5 RSNe and SNRs but the SSCs and their immediate surroundings are largely devoid of non-thermal radio sources. Even though many massive stars in the SSCs are expected to have exploded already, when compared with Mu200982 and its many SSCs the absence of RSNe and SNRs in and near A and B may seem plausible on statistical arguments. The absence of RSNe and SNRs in and near A and B may, however, also be due to a violent and turbulent outflow of stellar winds and supernova ejected material, which does not provide a quiescent environment for the development of SNRs within and near the SSCs.

The H(I) content of the advanced merger NGC4441

Aims. We investigate the distribution of molecular and atomic gas and the nature of the power source of the LINER (Low-Ionisation Nuclear Emission-line Region) activity in NGC 5218. Methods. We performed a multi wavelength study of the barred interacting LINER galaxy NGC 5218. We used the Owens Valley Radio Observatory to obtain interferometer data of CO 1–0, the Multi Element Radio Linked Interferometer for 1.4 GHz continuum and Hi-absorption, and the Onsala Space Observatory to obtain single dish data of CO 1–0, HCN 1–0 and HCO + 1–0. Results. Toward the center of the galaxy, we have detected a double CO peak. The peaks are separated by 2 �� (380 pc). The observed peaks appear to be caused by an almost edge-on ring of molecular gas with a radius of 470 pc and a rotational velocity of 140 km s −1 . We see no kinematical signs of a compact nuclear disc. However, there are kinematical signs of an expanding shell of molecular gas at the eastern side of the ring. The mass of the gas involved in the expansion is 7 × 10 7 M� , and we suggest that the expansion is driven by a burst of supernovae that took place some 5 × 10 6 years ago. We estimated that 10 000 supernovae were required to drive the expansion and that the corresponding number of supernovae per year was 0.002 over the age of the expanding shell. The radio continuum peak agrees well in space with the expanding molecular shell, and the Hi-absorption agrees well in both space and velocity, and supports the notion of an expanding shell. We find that the radio flux density and the bulk of the FIR are associated with nuclear, but slightly off-centre, star formation in the central R = 2 �� (380 pc). Conclusions. We suggest a scenario where shock fronts of the expanding shell shock heat the surrounding gas, and give rise to a LINER like spectrum. We conclude that the LINER activity observed in NGC 5218 is probably due to nuclear starburst activity, and not to AGN-activity. A fraction of the molecular gas in the bar, outside of the central region, appears to be in a different, gravitationally unbound phase, possibly on x2 orbits to the large scale optical bar.

Stars and gas in the Medusa merger

We present sub-arcsecond, Multi-Element Radio Linked Interferometer (MERLIN) observations of the decimetre radio continuum structure and neutral hydrogen (Hi) absorption from the nuclear region of the starburst galaxy NGCu20094194 (the Medusa Merger). The continuum structure of the central kiloparsec of the Medusa has been imaged, revealing a pair of compact radio components surrounded by more diffuse, weak radio emission. Using the constraints provided by these observations and those within the literature we conclude that the majority of this radio emission is related to the ongoing star-formation in this merger system. u2029With these observations we also trace deep Hi absorption across the detected radio continuum structure. The absorbing Hi gas structure exhibits large variations in column densities. The largest column densities are found toward the south of the nuclear radio continuum, co-spatial with both a nuclear dust lane and peaks in 12 COu2009(