HCN(1-0) OBSERVATIONS OF STARLESS CORES

SOHN J,,LEE C, W,,LEE H, M.,PARK Y.-S.,MYERS P. C.,LEE Y.,TAFALLA M. The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

We present a progress report on HCN(1-0) line observations toward starless cores to probe inward motions. We have made a single pointing survey toward the central regions of 85 starless cores and performed mapping observations of 6 infall candidate starless cores. The distributions of the velocity difference between HCN(1-0) hyperfine lines and the optically thin tracer $N_2H^+$(1-0) are significantly skewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to the blue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence than CS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infall asymmetry seen in HCN(1-0) hyperfine lines, CS(3-2), CS(2-1), $DCO^+(2-1)$ and $N_2H^+$ observations. The HCN(1-0) F(O-l) with the least optical depth usually shows a similar intensity distribution to that of $N_2H^+$ which closely traces the density distribution of the cores, indicating that HCN(1-0) is less chemically affected and so believed to reflect kinematics occurring in rather inner regions of the cores. Detailed radiative transfer model fits of the spectra are underway to analyze central infall kinematics in starless cores.

HCN(1-0) OBSERVATIONS OF STARLESS CORES

J. SOHN,C. W. LEE,H. M. LEE,Y.-S. PARK,P. C. MYERS,Y. LEE,M. TAFALLA 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

We present a progress report on HCN(1-0) line observations toward starless cores to probe inwardmotions. We have made a single pointing survey toward the central regions of 85 starless cores andperformed mapping observations of 6 infall candidate starless cores. The distributions of the velocitydierence between HCN(1-0) hyperne lines and the optically thin tracer N2H+ (1-0) are signicantlyskewed to the blue, meaning that HCN(1-0) frequently detects inward motions. Their skewness to theblue is even greater than that of CS(2-1) Lee et al., possibly implying more infall occurrence thanCS(1-0). We identify 19 infall candidates by using several characteristics illustrating spectral infallasymmetry seen in HCN(1-0) hyperne lines, CS(3-2), CS(2-1), DCO+ (2-1) and N2H+ observations.The HCN(1-0) F(0-1) with the least optical depth usually shows a similar intensity distribution to thatof N2H+ which closely traces the density distribution of the cores, indicating that HCN(1-0) is lesschemically aected and so believed to reect kinematics occurring in rather inner regions of the cores.Detailed radiative transfer model ts of the spectra are underway to analyze central infall kinematicsin starless cores.

ON THE GALACTIC SPIRAL PATTERNS: STELLAR AND GASEOUS

MARCO MARTOS,MIGUEL YAN?EZ,XAVIER HERNANDEZ,EDMUNDO MORENO,BARBARA PICHARDO 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

GLOBAL Hɪ PROPERTIES OF GALAXIES VIA SUPER-PROFILE ANALYSIS

Kim, Minsu,Oh, Se-Heon The Korean Astronomical Society 2022 Journal of The Korean Astronomical Society Vol.55 No.5

We present a new method which constructs an Hɪ super-profile of a galaxy which is based on profile decomposition analysis. The decomposed velocity profiles of an Hɪ data cube with an optimal number of Gaussian components are co-added after being aligned in velocity with respect to their centroid velocities. This is compared to the previous approach where no prior profile decomposition is made for the velocity profiles being stacked. The S/N improved super-profile is useful for deriving the galaxy's global Hɪ properties like velocity dispersion and mass from observations which do not provide sufficient surface brightness sensitivity for the galaxy. As a practical test, we apply our new method to 64 high-resolution Hɪ data cubes of nearby galaxies in the local Universe which are taken from THINGS and LITTLE THINGS. In addition, we also construct two additional Hɪ super-profiles of the sample galaxies using symmetric and all velocity profiles of the cubes whose centroid velocities are determined from Hermite h3 polynomial fitting, respectively. We find that the Hɪ super-profiles constructed using the new method have narrower cores and broader wings in shape than the other two super-profiles. This is mainly due to the effect of either asymmetric velocity profiles' central velocity bias or the removal of asymmetric velocity profiles in the previous methods on the resulting Hɪ super-profiles. We discuss how the shapes (𝜎_n/𝜎_b, A_n/A_b, and A_n/A_tot) of the new Hɪ super-profiles which are measured from a double Gaussian fit are correlated with star formation rates of the sample galaxies and are compared with those of the other two super-profiles.

INWARD MOTIONS IN STARLESS CORES TRACED WITH CS (3-2) and (2-1) LINES

LEE CHANG WON,MYERS PHILIP C.,PLUME RENE The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines to study inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect to $N_2H^+$ are found to correlate well with each other and to have similar number distributions, implying that, in many cores, systematic inward motions of gaseous material may occur over a range of density of at least a factor ${\~}$4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidates suggest that the median effective line-of-sight speed of the inward-moving gas is ${\~}0.07 km\;s^{-l}$ for CS (3-2) and ${\~} 0.04 km\;s^{-l}$ for CS(2-1). Considering that the optical depth obtained from the fits is usually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, denser gas with greater inward motions than CS(2-1) implying that many of the infall candidates have faster infall toward the center. However, this conclusion may not be representative of all starless core infall candidates, due to the statistically small number analyzed here. Further line observations will be useful to test this conclusion.

The H <small>i</small> environment of counter‐rotating gas hosts: gas accretion from cold gas blobs

Chung, Aeree,Bureau, Martin,van Gorkom, J. H.,Koribalski, Bä,rbel Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.422 No.2

<P><B>ABSTRACT</B></P><P>We probe the H <SMALL>i</SMALL> properties and the gas environments of three early‐type barred galaxies harbouring counter‐rotating ionized gas: NGC 128, NGC 3203 and NGC 7332. Each system has one or more optically identified galaxy at a similar or as yet unknown redshift within a 50‐kpc projected radius. Using H <SMALL>i</SMALL> synthesis imaging data, we investigate the hypothesis that the counter‐rotating gas in these galaxies has been accreted from their neighbours. In NGC 128 and NGC 3203, we find 9.6 × 10<SUP>7</SUP> and 2.3 × 10<SUP>8</SUP> M<SUB>⊙</SUB> of H <SMALL>i</SMALL>, respectively, covering almost the entire stellar bodies of dwarf companions that appear physically connected. Both the H <SMALL>i</SMALL> morphology and kinematics are suggestive of tidal interactions. In NGC 7332, we do not find any directly associated H <SMALL>i</SMALL>. Instead, NGC 7339, a neighbour of a comparable size at about 10 kpc, is found with 8.9 × 10<SUP>8</SUP> M<SUB>⊙</SUB> of H <SMALL>i</SMALL> gas. More recently in a single dish observation, however, another group discovered a large H <SMALL>i</SMALL> structure which seems to be an extension of NGC 7339’s H <SMALL>i</SMALL> disc and also covers NGC 7332. All these observations thus suggest that H <SMALL>i</SMALL> gas is being accreted in these three galaxies from their companions, which is likely responsible for the kinematically decoupled gas component present in their central region. In particular, the dynamical friction time‐scales of the nearest neighbours with H <SMALL>i</SMALL> gas of NGC 128 and NGC 3203 are comparable to their orbital time‐scales around the counter‐rotators, several ∼10<SUP>8</SUP> yr, implying that those neighbours will likely soon merge with the primary galaxies, fuelling them with gas. NGC 7332 also appears to be in the merging process with its neighbour through the common H <SMALL>i</SMALL> envelope. Besides, we find some other potential gas donors around NGC 128 and NGC 7332: two H <SMALL>i</SMALL>‐rich galaxies with <IMG src='/wiley-blackwell_img/equation/MNR_20679_mu1.gif' alt ='inline image'/> and 2.5 × 10<SUP>9</SUP> M<SUB>⊙</SUB> at a distance of ≈67 kpc from NGC 128 and two dwarf systems with <I>M</I><SUB>HI</SUB>= 3.9 × 10<SUP>7</SUP> and 7.4 × 10<SUP>7</SUP> M<SUB>⊙</SUB> at ≲100 kpc from NGC 7332. Among the seven H <SMALL>i</SMALL> features identified in this study, three of them are associated with dwarf galaxies, two of which have only been recently identified in a blind survey, while the third one is still not catalogued at optical wavelengths. Considering the incompleteness of existing studies of the faint dwarf galaxy population both in the optical and in H <SMALL>i</SMALL>, accretion from cold gas blobs, presumably gas‐rich dwarfs, is expected to occur even more frequently than what is inferred from such cases that have been observed to date.</P>

KINEMATICAL PROPERTIES OF PLANETARY NEBULAE WITH WR-TYPE NUCLEI

DANEHKAR, ASHKBIZ,STEFFEN, WOLFGANG,PARKER, QUENTIN A. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

We have carried out integral field unit (IFU) spectroscopy of $H{\alpha}$, [$N{\small{II}}$] and [$O{\small{III}}$] emission lines for a sample of Galactic planetary nebulae (PNe) with Wolf-Rayet (WR) stars and weak emission-line stars (wels). Comparing their spatially-resolved kinematic observations with morpho-kinematic models allowed us to disentangle their three-dimensional gaseous structures. Our results indicate that these PNe have axisymmetric morphologies, either bipolar or elliptical. In many cases the associated kinematic maps for the PNe around hot central stars also reveal the presence of so-called fast low-ionization emission regions.

INWARD MOTIONS IN STARLESS CORES TRACED WITH CS (3-2) AND (2-1) LINES

CHANG WON LEE,PHILIP C. MYERS,RENE? PLUME 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

We compare the results of the surveys of starless cores performed with CS (2-1) and (3-2) lines tostudy inward motions in the cores. The velocity shifts of the CS(3-2) and (2-1) lines with respect toN2H+ are found to correlate well with each other and to have similar number distributions, implyingthat, in many cores, systematic inward motions of gaseous material may occur over a range of density ofat least a factor 4. Fits of the CS spectra to a 2-layer radiative transfer model in ten infall candidatessuggest that the median eective line-of-sight speed of the inward-moving gas is 0:07 km s1 forCS (3-2) and 0:04 km s1 for CS(2-1). Considering that the optical depth obtained from the ts isusually smaller in CS(3-2) than in (2-1) line, this may indicate that CS(3-2) usually traces inner, densergas with greater inward motions than CS(2-1) implying that many of the infall candidates have fasterinfall toward the center. However, this conclusion may not be representative of all starless core infallcandidates, due to the statistically small number analyzed here. Further line observations will be usefulto test this conclusion.

ON THE ORIGIN OF THE NEUTRAL HYDROGEN SUPERSHELLS

Elias, Federico,Silich, Sergiy,Franco, Jose The Korean Astronomical Society 2007 Journal of The Korean Astronomical Society Vol.40 No.4

Here we analyze if the ionized shells associated with giant HII regions represent the progenitors of the larger neutral hydrogen supershells detected in the Milky Way and other spiral and dwarf irregular galaxies. We calculate the evolutionary tracks that 12 HII shells found by Relano et al. (2005, 2007) would have if they expanded into the interstellar medium because of multiple supernovae explosions occurring inside the cavity. We find, contrary to Relano et al. (2007), that the evolutionary tracks of these HII shells are inconsistent with the observed parameters of the largest and most massive neutral hydrogen supershells. Thus, an additional energy source to the multiple supernovae explosions is required in order to explain the origin of the most massive neutral hydrogen shells.

FORMATION OF INTERMEDIATE-SCALE STRUCTURES IN SPIRAL GALAXIES

WOONG-TAE KIM 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

Disk galaxies abound with intermediate-scale structures such as OB star complexes, giant clouds, anddust spurs in a close geometrical association with spiral arms. Various mechanisms have been proposedas candidates for their origin, but a comprehensive theory should encompass fundamental physical agentssuch as self-gravity, magnetic elds, galactic dierential rotation, and spiral arms, all of which are knownto exist in disk galaxies. Recent numerical simulations incorporating all these physical processes showthat magneto-Jeans instability (MJI), in which magnetic tension resists the stabilizing Coriolis force ofgalaxy rotation, is much more powerful than swing-amplication or the Parker instability in forming self-gravitating intermediate-scale structures. The MJI occurring in shearing and expanding ows o spiralarms rapidly forms structures elongated along the direction perpendicular to the arms, remarkablysimilar to dust spurs seen inHST images of spiral galaxies. In highly nonlinear stages, these spursfragment to form bound clumps, possibly evolving into bright arm and interarm HI regions, suggestingthat all these intermediate-scale structures in spiral galaxies probably share a common dynamical origin.