Sabine König

ALMA OBSERVATIONS OF WARM DENSE GAS IN NGC 1614-BREAKING OF THE STAR FORMATION LAW IN THE CENTRAL KILOPARSEC

Recently, research performed by two groups has revealed that the magnetar spin-down energy injection model with full energy trapping can explain the early-time light curves of SN 2010gx, SN 2013dg, LSQ12dlf, SSS120810, and CSS121015 but fails to fit the late-time light curves of these superluminous supernovae (SLSNe). These results imply that the original magnetar-powered model is challenged in explaining these SLSNe. Our paper aims to simultaneously explain both the early-and late-time data/upper limits by considering the leakage of hard emissions. We incorporate quantitatively the leakage effect into the original magnetar-powered model and derive a new semianalytical equation. Comparing the light curves reproduced by our revised magnetar-powered model with the observed data and/or upper limits of these five SLSNe, we found that the late-time light curves reproduced by our semianalytical equation are in good agreement with the late-time observed data and/or upper limits of SN 2010gx, CSS121015, SN 2013dg, and LSQ12dlf and the late-time excess of SSS120810, indicating that the magnetar-powered model might be responsible for these SLSNe and that the gamma-ray and X-ray leakages are unavoidable when the hard photons were down-Comptonized to softer photons. To determine the details of the leakage effect and unveil the nature of SLSNe, more high-quality bolometric light curves and spectra of SLSNe are required.

Spatially Resolved CO SLED of the Luminous Merger Remnant NGC 1614 with ALMA

We present high-resolution (1.”0) Atacama Large Millimeter/submillimeter Array (ALMA) observations of CO (1–0) and CO (2–1) rotational transitions toward the nearby IR-luminous merger NGC 1614 supplemented with ALMA archival data of CO (3–2) and CO (6–5) transitions. The CO (6–5) emission arises from the starburst ring (central 590 pc in radius), while the lower-J CO lines are distributed over the outer disk (~3.3 kpc in radius). Radiative transfer and photon-dominated region (PDR) modeling reveals that the starburst ring has a single warmer gas component with more a intense far-ultraviolet radiation field (n_(H_2) ~ 10^(4.6) Cm^(−3), T_(kin) ~ 42 K, and G_0 ~ 10^(2.7)) relative to the outer disk (N_(H_2) ~ 10^(5.1) cm^(−3), T_(kin) ~ 22 K, and G_0 ~ 10^(0.9)). A two-phase molecular interstellar medium with a warm and cold (>70 and ~19 K) component is also an applicable model for the starburst ring. A possible source for heating the warm gas component is mechanical heating due to stellar feedback rather than PDR. Furthermore, we find evidence for non-circular motions along the north–south optical bar in the lower-J CO images, suggesting a cold gas inflow. We suggest that star formation in the starburst ring is sustained by the bar-driven cold gas inflow and that starburst activities radiatively and mechanically power the CO excitation. The absence of a bright active galactic nucleus can be explained by a scenario where cold gas accumulating on the starburst ring is exhausted as the fuel for star formation or is launched as an outflow before being able to feed to the nucleus.

Deep ALMA imaging of the merger NGC 1614: Is CO tracing a massive inflow of non-starforming gas?

Aims. Observations of the molecular gas over scales of ~0.5 to several kpc provide crucial information on how molecular gas moves through galaxies, especially in mergers and interacting systems, where it ultimately reaches the galaxy center, accumulates, and feeds nuclear activity. Studying the processes involved in the gas transport is one of the important steps forward to understand galaxy evolution. Methods. ^(12)CO, ^(13)CO, and C^(18)O 1−0 high-sensitivity ALMA observations (~4′′ × 2′′) were used to assess the properties of the large-scale molecular gas reservoir and its connection to the circumnuclear molecular ring in the merger NGC 1614. Specifically, the role of excitation and abundances were studied in this context. We also observed the molecular gas high-density tracers CN and CS. Results. The spatial distributions of the detected ^(12)CO 1−0 and ^(13)CO 1−0 emission show significant differences. ^(12)CO traces the large-scale molecular gas reservoir, which is associated with a dust lane that harbors infalling gas, and extends into the southern tidal tails. ^(13)CO emission is for the first time detected in the large-scale dust lane. In contrast to ^(12)CO, its line emission peaks between the dust lane and the circumnuclear molecular ring. A ^(12)CO-to-^(13)CO 1−0 intensity ratio map shows high values in the ring region (~30) that are typical for the centers of luminous galaxy mergers and even more extreme values in the dust lane (>45). Surprisingly, we do not detect C^(18)O emission in NGC 1614, but we do observe gas emitting the high-density tracers CN and CS. Conclusions. We find that the ^(12)CO-to-^(13)CO 1−0 line ratio in NGC 1614 changes from >45 in the 2 kpc dust lane to ~30 in the starburst nucleus. This drop in ratio with decreasing radius is consistent with the molecular gas in the dust lane being kept in a diffuse, unbound state while it is being funneled toward the nucleus. This also explains why there are no (or very faint) signs of star formation in the dust lane, despite its high ^(12)CO luminosity. In the inner 1.5 kpc, the gas is compressed into denser and most likely self-gravitating clouds (traced by CN and CS emission), allowing it to power the intense central starburst. We find a high ^(16)O-to-^(18)O abundance ratio in the starburst region (≥900), typical of quiescent disk gas. This is surprising because by now, the starburst is expected to have enriched the nuclear interstellar medium in ^(18)O relative to ^(16)O. We suggest that the massive inflow of gas may be partially responsible for the low ^(18)O/^(16)O abundance since it will dilute the starburst enrichment with unprocessed gas from greater radial distances. The ^(12)CO-to-^(13)CO abundance of >90 we infer from the line ratio is consistent with this scenario. It suggests that the nucleus of NGC 1614 is in a transient phase of its evolution where the starburst and the nuclear growth is still being fuelled by returning gas from the minor merger event.

Subarcsecond imaging of the water emission in Arp 220

Aims Extragalactic observations of water emission can provide valuable insights into the excitation of the interstellar medium. In particular they allow us to investigate the excitation mechanisms in obscured nuclei, i.e. whether an active galactic nucleus or a starburst dominate. Methods We use sub-arcsecond resolution observations to tackle the nature of the water emission in Arp 220. ALMA Band 5 science verification observations of the 183 GHz H2O 313-220 line, in conjunction with new ALMA Band 7 H2O 515-422 data at 325 GHz, and supplementary 22 GHz H2O 616 - 523 VLA observations, are used to better constrain the parameter space in the excitation modelling of the water lines. Results We detect 183 GHz H2O and 325 GHz water emission towards the two compact nuclei at the center of Arp 220, being brighter in Arp 220 West. The emission at these two frequencies is compared to previous single-dish data and does not show evidence of variability. The 183 and 325 GHz lines show similar spectra and kinematics, but the 22 GHz profile is significantly different in both nuclei due to a blend with an NH3 absorption line. Conclusions Our findings suggest that the most likely scenario to cause the observed water emission in Arp 220 is a large number of independent masers originating from numerous star-forming regions.

Molecular tendrils feeding star formation in the Eye of the Medusa - The Medusa merger in high resolution 12CO 2–1 maps

Studying molecular gas properties in merging galaxies gives us important clues to the onset and evolution of interaction-triggered starbursts. NGC 4194 (the Medusa merger) is particularly interesting to study, since its FIR-to-CO luminosity ratio rivals that of ultraluminous galaxies (ULIRGs), despite its lower luminosity compared to ULIRGs, which indicates a high star formation efficiency (SFE) that is relative to even most spirals and ULIRGs. We study the molecular medium at an angular resolution of 0.65 �� × 0.52 �� (∼120 × 98 pc) through our observations of 12 CO 2−1 emission using the Submillimeter Array (SMA). We compare our 12 CO 2−1 maps with the optical Hubble Space Telescope and high angular resolution radio continuum images to study the relationship between molecular gas and the other components of the starburst region. The molecular gas is tracing the complicated dust lane structure of NGC 4194 with the brightest emission being located in an off-nuclear ring-like structure with ∼320 pc radius, the Eye of the Medusa. The bulk CO emission of the ring is found south of the kinematical center of NGC 4194. The northern tip of the ring is associated with the galaxy nucleus, where the radio continuum has its peak. Large velocity widths associated with the radio nucleus support the notion of NGC 4194 hosting an active galactic nucleus. A prominent, secondary emission maximum in the radio continuum is located inside the molecular ring. This suggests that the morphology of the ring is partially influenced by massive supernova explosions. From the combined evidence, we propose that the Eye of the Medusa contains a shell of swept up material where we identify a number of giant –

Hidden molecular outflow in the LIRG Zw 049.057

Context. Feedback in the form of mass outflows driven by star formation or active galactic nuclei is a key component of galaxy evolution. The luminous infrared galaxy Zw 049.057 harbours a compact obscured nucleus with a possible far-infrared signature of outflowing molecular gas. Due to the high optical depths at far-infrared wavelengths, however, the interpretation of the outflow signature is uncertain. At millimeter and radio wavelengths, the radiation is better able to penetrate the large columns of gas and dust responsible for the obscuration. Aims. We aim to investigate the molecular gas distribution and kinematics in the nucleus of Zw 049.057 in order to confirm and locate the molecular outflow, with the ultimate goal to understand how the nuclear activity affects the host galaxy. Methods. We used high angular resolution observations from the Submillimeter Array (SMA), the Atacama Large Millimeter/submillimeter Array (ALMA), and the Karl G. Jansky Very Large Array (VLA) to image the CO J = 2-1 and J = 6-5 emission, the 690 GHz continuum, the radio centimeter continuum, and absorptions by rotationally excited OH. Results. The CO line profiles exhibit wings extending ~ 300 km s -1 beyond the systemic velocity. At centimeter wavelengths, we find a compact (~ 40 pc) continuum component in the nucleus, with weaker emission extending several 100 pc approximately along the major and minor axes of the galaxy. In the OH absorption lines toward the compact continuum, wings extending to a similar velocity as for the CO are only seen on the blue side of the profile. The weak centimeter continuum emission along the minor axis is aligned with a highly collimated, jet-like dust feature previously seen in near-infrared images of the galaxy. Comparison of the apparent optical depths in the OH lines indicate that the excitation conditions in Zw 049.057 differ from those within other OH megamaser galaxies. Conclusions. We interpret the wings in the spectral lines as signatures of a nuclear molecular outflow. A relation between this outflow and the minor axis radio feature is possible, although further studies are required to investigate this possible association and understand the connection between the outflow and the nuclear activity. Finally, we suggest that the differing OH excitation conditions are further evidence that Zw 049.057 is in a transition phase between megamaser and kilomaser activity.

Atomic hydrogen bridge fueling NGC 4418 with gas from VV 655

Context. The galaxy NGC4418 harbours a compact (< 20 pc) core with a very high bolometric luminosity (similar to 10(11) L-circle dot). As most of the galaxy energy output comes from this small region, it is of interest to determine what fuels this intense activity. An interaction with the nearby blue irregular galaxy VV655 has been proposed, where gas acquired by NGC4418 could trigger intense star formation and / or black hole accretion in the centre. Aims. We aim to constrain the interaction hypothesis by studying neutral hydrogen structures that could reveal tails and debris connecting NGC4418 to the nearby galaxy VV655. Methods. We present observations at 1.4GHz with the Very Large Array (VLA) of the radio continuum as well as emission and absorption from atomic hydrogen. Gaussian distributions are fitted to observed HI emission and absorption spectra. We estimate the star formation rates (SFRs) of NGC4418 and VV655 from the 1.4 GHz radio emission and compare them with estimates from archival 70 mu m Herschel observations. Results. An atomic HI bridge is seen in emission, connecting NGC4418 to the nearby galaxy VV655. An HI tail is also seen extending south-west from VV655. While NGC4418 is bright in continuum emission and seen in HI absorption, VV655 is barely detected in the continuum, but shows bright HI emission (M-HI similar to 10(9) M-circle dot). We estimate SFRs from the 1.4 GHz continuum of 3 : 2 M circle dot yr(-1) and 0 : 13 M(circle dot)yr(-1) for NGC4418 and VV655, respectively. Systemic HI velocities of 2202 +/- 20 km s(-1) (emission) and 2105 : 4 +/- 10 km s(-1) (absorption) are measured for VV655 and NGC4418, respectively. Redshifted HI absorption is seen (v(c) = 2194 : 0 +/- 4 : 4 km s(-1)) towards NGC4418, suggesting gas infall. North-west of NGC4418, we detect HI in emission, blueshifted (v(c) = 2061 : 9 +/- 5 : 1 km s(-1)) with respect to NGC4418, consistent with an outflow perpendicular to the galaxy disk. We derive a deprojected outflow speed of 178 km S-1, which, assuming a simple cylindrical model, gives an order-of-magnitude estimate of the HI mass outflow rate of 2 : 5 M(circle dot)y(r-)1. Conclusions. The morphology and velocity structure seen in HI is consistent with an interaction scenario where gas was transferred from VV655 to NGC4418. We argue that the galaxies have passed each other once, about 190 M-circle dot ago, and that this interaction has caused the tidal HI bridge and HI tail seen today. Some gas is falling towards NGC4418, and may fuel the activity in the centre. We interpret blueshifted HI-emission north-west of NGC4418 as a continuation of the outflow previously reported on smaller scales, powered by star formation an /or black hole accretion in the centre.

CI, [CII] and CO observations towards TNJ 1338–1942: Probing the ISM in a massive proto-cluster galaxy at z = 4.11

A number of studies have dealt with the link between distant powerful radio sources and the most massive galaxies in the early Universe. Despite major advances in our understanding of high redshift radio galaxies (HzRGs), we still only have a rudimentary picture of the physical conditions (i.e. gas density, temperature, ambient UV-field) prevailing in the interstellar medium (ISM) of these objects. Here we report on ongoing CI, [CII] and CO observations of TNJ 1338–1942 at z = 4.11 with the IRAM 30m telescope, the JCMT and ATCA. With these observations we will make a first attempt at constraining the average ISM conditions in TNJ 1338–1942.