Rainer Mauersberger

A 2 Millimeter Spectral Line Survey of the Starburst Galaxy NGC 253

We present the first unbiased molecular line survey toward an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 GHz, i.e., most of the 2 mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers 34SO and HC18O+. Tentative detections of two deuterated species, DNC and N2D+, are reported for the first time from a target beyond the Magellanic Clouds. In addition, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.We present the first unbiased molecular line survey towards an extragalactic source, namely the nuclear region of the starburst galaxy NGC 253. The scan covers the frequency band from 129.1 to 175.2 GHz, i.e. most of the 2mm atmospheric window. We identify 111 spectral features as transitions from 25 different molecular species. Eight of which (three tentatively) are detected for the first time in the extragalactic interstellar medium. Among these newly detected species, we detected the rare isotopomers 34SO and HC18O+. Tentative detections of two deuterated species, DNC and N2D+, are reported for the first time from a target beyond the Magellanic Clouds. Additionally, three hydrogen recombination lines are identified, while no organic molecules larger than methanol are detected. Column densities and rotation temperatures are calculated for all the species, including an upper limit to the ethanol abundance. A comparison of the chemical composition of the nuclear environment of NGC 253 with those of selected nearby galaxies demonstrates the chemical resemblance of IC 342 and NGC 4945 to that of NGC 253. On the other hand, the chemistries characterizing NGC 253 and M 82 are clearly different. We also present a comparison of the chemical composition of NGC 253 with those observed in Galactic prototypical sources. The chemistry of NGC 253 shows a striking similarity with the chemistry observed toward the Galactic center molecular clouds, which are thought to be dominated by low-velocity shocks. This resemblance strongly suggests that the heating in the nuclear environment of NGC 253 is dominated by the same mechanism as that in the central region of the Milky Way.

Dense gas in nearby galaxies - XV. Hot ammonia in NGC 253, Maffei 2 and IC 342

The detection of NH3 inversion lines up to the ( J; K) = (6; 6) level is reported toward the central regions of the nearby galaxies NGC 253, Maei 2, and IC 342. The observed lines are up to 406 K (for (J; K)= (6; 6)) and 848 K (for the (9; 9) transition) above the ground state and reveal a warm (Tkin = 100:::140 K) molecular component toward all galaxies studied. The tentatively detected ( J; K) = (9; 9) line is evidence for an even warmer (>400 K) component toward IC 342. Toward NGC 253, IC 342 and Maei 2 the global beam averaged NH3 abundances are 1 2 10 8 , while the abundance relative to warm H2 is around 10 7 . The temperatures and NH3 abundances are similar to values found for the Galactic central region. C-shocks produced in cloud-cloud collisions can explain kinetic temperatures and chemical abundances. In the central region of M 82, however, the NH3 emitting gas component is comparatively cool (30 K). It must be dense (to provide sucient NH3 excitation) and well shielded from dissociating photons and comprises only a small fraction of the molecular gas mass in M 82. An important molecular component, which is warm and tenuous and characterized by a low ammonia abundance, can be seen mainly in CO. Photon dominated regions (PDRs) can explain both the high fraction of warm H2 in M 82 and the observed chemical abundances.

The molecular cores in the L1287, AFGL 5142, and IRAS 20126 + 4104 regions

The NH 3 (J, K)=(1, 1) and (2, 2) line emission was mapped toward three regions with molecular outflows, L1287, AFGL 5142, and IRAS 20126+4104, using the Effelsberg 100 m telescope. Additional C 18 O (J=2→1) and CS (J=3→2) observations of L1287 were carried out with the IRAM 30 m telescope. For the three regions, the high-density molecular core, as traced by the ammonia emission, peaks very close to the position of the proposed powering sources of the outflows. In AFGL 5142 we flavor the radio continuum source proposed by Torrelles et al. (1992b) as the powering source of the outflow. The molecular cores best resolved by the telescope beam are elongated in a direction perpendicular to the outflow axis

Dense molecular gas in galactic nuclei

SummaryThe nuclear regions of many galaxies are not accessible at optical wavelengths and are devoid of HI, but contain large quantities of molecular gas and dust. With recent advances in instrumentation it is now possible to probe the kinematics and physical state of the cool dense interstellar medium, thus providing a new and important tool to investigate the circumnuclear gas in galaxies that are more ‘active’ than our own. The scope of this review is to summarize results related to the subject with an emphasis on observational data. Sects. 1 and 2 present a general introduction, followed by a discussion of molecular mass estimates. In Sect. 3 correlations between nuclear and global galactic properties are discussed. Sects. 4 and 5 summarize observational results for nearby strongly interacting galaxies, properties of molecular bars and rings, and theoretical advances in modelling the data. The main part of the review (Sects. 6–8) describes the kinematics and the physical and chemical properties of the dense gas, including masers, and compares them with the nuclear region of the Galaxy. Molecular gas in distant galaxies and the evolution of active galaxies are discussed in Sect. 9. Some promising avenues for future research are outlined in Sect. 10.

A highly collimated outflow in the core of OMC-1

The paper reports the discovery of a 120 arcsec long jet of CO in OMC-1. The feature, which is redshifted up to 15 km s-1 from the ambient CO gas, was presumably ejected from CS3/FIR4 60 arcsec southwest of the Trapezium and 110 arcsec south of IRc2. It might be related to a local bipolar source recently found there in SiO. The jet has very narrow width (not greater than 8 arcsec) and shows no sign of angular divergence; its axis is a straight line. The matter is accelerated all along, with the largest accelerations observed on the central axis. Lower velocity material envelops the high-speed core. Halfway along the jet, there is a sharp break at which the higher velocities terminate abruptly. Beyond the break, acceleration continues without change of direction or strength; the flows final disappearance might be caused by accelerative dilution. The jet is probably denser than the ambient cloud; its temperature (about 45 K) approaches ambient values. Blueshifted emission of narrow lateral extent is seen over the full length of the redshifted jet. 15 refs.

The powering sources of the molecular outflows in the AFGL 437, AFGL 5142, and AFGL 5157 regions

VLA 3.6 cm continuum and water maser observations are presented toward the central region of three molecular outflows for which the position of the powering sources was not clearly established: AFGL 437, AFGL 5142, and AFGL 5157. In these regions, continuum and H 2 O maser emission has been detected near the peak of the associated high-density molecular cores. These data indicate a close association between the molecular cores, the radio continuum sources, and the H 2 O masers

A new bipolar outflow source in OMC-1

Observations of the J = 2-1 and J = 5-4 transitions of SiO have been made toward the outflow source about 1.5 arcmin south of Orion-KL, using the IRAM 30-m telescope, with 25- and 13-arcsec resolution, respectively. Additional measurements of the J = 2-1, 3-2, and 5-4 lines of C34S and observations of J = 5-4 and J = 13-12 transitions of CH{sub 3}CN have been made with the 30-m telescope. The SiO data clearly indicate that a separate outflow source exists about 100 arcsec S and 20 arcsec W of the Orion-KL/IRc2 position. 17 refs.

High-density molecular gas in external galaxies: formaldehyde and carbon monosulfide

Observations in the 2(11)-2(12) transition of orthoformaldehyde were made to search for high-density gas in extragalactic sources. The line was detected in absorption toward NGC 253 and in emission toward M82, the first detection of 2 cm emission outside the Galaxy. A comparison of the 2 and 6 cm lines from Cen A indicates densities of the order of 100,000/cu cm. Comparison of the 2 and 6 cm lines from NGC 253 suggests that the central part of the 6 cm profile consists of a superposition of a broad absorption line and a narrower emission component. The emission probably originates in foreground formaldehyde gas pumped by the nonthermal radio continuum from the nucleus. In M82, a high angular resolution CS map shows two spatially unresolved centers of emission located along the major axis of the galaxy. The two emission centers are a part of the molecular torus structure also seen in CO. Extragalactic paraformaldehyde was detected for the first time. 43 refs.

Interstellar CNO isotope Ratios

In an interpretation of interstellar, circumstellar, and solar system CNO isotope ratios, we find two scenarios which are free of internal inconsistencies. The first requires that the early solar system was enriched by material from massive stars, leading to enhanced 12C/13C and 18O/17O ratios and to a reduced 14N/15N ratio. The second involves infall of gas onto the galactic disk after the formation of the solar system. Both scenarios require that the bulk of the interstellar 16O, 18O and 15N originates from massive stars (>8M⊙), with 18O and perhaps 15N being destroyed in lower mass stars. 17O is mainly synthesized in stars of intermediate mass while 12C, 13C, and 14N are produced in stars of high and intermediate masses.

A Very Straight And Collimated Outflow In The Core

We have recently discovered a large-scale (200”) outflow system in the core of OMC-1 (fig. 1), centered about 100” South of IRc2 and extending over some 120” (red lobe) resp. 60” (blue) along a position angle of —31°Schmid-Burgk et al. 1990). The blue lobe which might actually trude into the Ell region M42is poorly defined in CO 2-1, but the red lobe reveals a number of remarkable properties which we summarize here: