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.

EVOLUTION OF THE SPIN OF LATE-TYPE GALAXIES CAUSED BY GALAXY-GALAXY INTERACTIONS

Hwang, Jeong-Sun,Park, Changbom,Nam, Soo-hyeon,Chung, Haeun The Korean Astronomical Society 2021 Journal of The Korean Astronomical Society Vol.54 No.2

We use N-body/hydrodynamic simulations to study the evolution of the spin of a Milky Way-like galaxy through interactions. We perform a controlled experiment of co-planar galaxy-galaxy encounters and study the evolution of disk spins of interacting galaxies. Specifically, we consider cases where the late-type target galaxy encounters an equally massive companion galaxy, which has either a late or an early-type morphology, with a closest approach distance of about 50 kpc, in prograde or retrograde sense. By examining the time change of the circular velocity of the disk material of the target galaxy from each case, we find that the target galaxy tends to lose the spin through prograde collisions but hardly through retrograde collisions, regardless of the companion galaxy type. The decrease of the spin results mainly from the deflection of the orbit of the disk material by tidal disruption. Although there is some disk material which gains the circular velocity through hydrodynamic as well as gravitational interactions or by transferring material from the companion galaxy, it turns out that the amount of the material is generally insufficient to increase the overall galactic spin under the conditions we set. We find that the spin angular momentum of the target galaxy disk decreases by 15-20% after a prograde collision. We conclude that the accumulated effects of galaxy-galaxy interactions will play an important role in determining the total angular momentum of late-type galaxies.

PRE-PROCESSING OF GALAXIES IN THE FILAMENTS AROUND THE VIRGO CLUSTER

YOON, HYEIN,CHUNG, AEREE,SENGUPTA, CHANDREYEE,WONG, O. IVY,BUREAU, MARTIN,REY, SOO-CHANG,VAN GORKOM, J.H. The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2

Galaxies can be "pre-processed" in the low-density outskirts by ambient medium in the filaments or tidal interactions with other galaxies while falling into the cluster. In order to probe how early on and by which mechanisms galaxies can be affected before they enter high-density cluster environments, we are carrying out an atomic hydrogen ($H\small{I}$) imaging study of a sample of galaxies selected from three filamentary structures around the Virgo cluster. Our sample consists of 14 late-type galaxies, which are potentially interacting with their surroundings. The $H\small{I}$ observations have been done using the Westerbork Synthesis Radio Telescope, the Giant Metrewave Radio Telescope, and the Jansky Very Large Array with column density sensitivity of ${\approx}3-5{\times}10^{19}cm^{-2}$ in $3{\sigma}$ per channel, which is low enough to detect faint $H\small{I}$ features in the outer disks of galaxies. In this work, we present the Hi data of two galaxies that were observed with GMRT. We examine the $H\small{I}$ morphology and kinematics to find the evidence for gas-gas and/or tidal interactions, and discuss which mechanism(s) could be responsible for pre-processing in these cases.

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.

SPATIALLY RESOLVED KINEMATICS OF GAS AND STARS IN HIDDEN TYPE 1 AGNS

Son, Donghoon,Woo, Jong-Hak,Eun, Da-In,Cho, Hojin,Karouzos, Marios,Park, Songyeon The Korean Astronomical Society 2020 Journal of The Korean Astronomical Society Vol.53 No.5

We analyze the spatially resolved kinematics of gas and stars for a sample of ten hidden type 1 AGNs in order to investigate the nature of their central sources and the scaling relation with host galaxy stellar velocity dispersion. We select our sample from a large number of hidden type 1 AGNs, which are identified based on the presence of a broad (full width at half maximum ≳1000 km s^-1) component in the Hα line profile and which are frequently mis-classified as type 2 AGNs because AGN continuum and broad emission lines are weak or obscured in the optical spectral range. We used the Blue Channel Spectrograph at the 6.5-m Multiple Mirror Telescope to obtain long-slit data with a spatial scale of 0.3 arcsec pixel^-1. We detected broad Hβ lines for only two targets; however, the presence of strong broad Hα lines indicates that the AGNs we selected are all low-luminosity type 1 AGNs. We measured the velocity, velocity dispersion, and flux of stellar continuum and gas emission lines (i.e., Hβ and [O III]) as a function of distance from the center. The spatially resolved gas kinematics traced by Hβ or [O III] are generally similar to the stellar kinematics except for the inner center, where signatures of gas outflows are detected. We compare the luminosity-weighted effective stellar velocity dispersions with the black hole masses and find that our hidden type 1 AGNs, which have relatively low back hole masses, follow the same scaling relation as reverberation-mapped type 1 AGN and more massive inactive galaxies.

FORMATION OF INTERMEDIATE-SCALE STRUCTURES IN SPIRAL GALAXIES

KIM WOONG-TAE The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

Disk galaxies abound with intermediate-scale structures such as OB star complexes, giant clouds, and dust spurs in a close geometrical association with spiral arms. Various mechanisms have been proposed as candidates for their origin, but a comprehensive theory should encompass fundamental physical agents such as self-gravity, magnetic fields, galactic differential rotation, and spiral arms, all of which are known to exist in disk galaxies. Recent numerical simulations incorporating all these physical processes show that magneto-Jeans instability (MJI), in which magnetic tension resists the stabilizing Coriolis force of galaxy rotation, is much more powerful than swing-amplification or the Parker instability in forming self-gravitating intermediate-scale structures. The MJI occurring in shearing and expanding flows off spiral arms rapidly forms structures elongated along the direction perpendicular to the arms, remarkably similar to dust spurs seen in HST images of spiral galaxies. In highly nonlinear stages, these spurs fragment to form bound clumps, possibly evolving into bright arm and interarm H II regions, suggesting that all these intermediate-scale structures in spiral galaxies probably share a common dynamical origin.

ARE GALACTIC WARPS INDUCED BY INTERGALACTIC FLOWS?

F. J. SÁNCHEZ-SALCEDO 한국천문학회 2004 Journal of The Korean Astronomical Society Vol.37 No.5

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanismof the generation of galactic warps. Here we discuss conditions under which intergalactic ows canbe relevant for warping eld galaxies. Constraints include the heating of the outer disk, the level ofasymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, thesymmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and thespeed of the intergalactic ow whether subsonic or supersonic. These constraints are discussed in thispaper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequenceof accretion ows onto the disk.

ARE GALACTIC WARPS INDUCED BY INTERGALACTIC FLOWS?

SANCHEZ-SALCEDO F. J. The Korean Astronomical Society 2004 Journal of The Korean Astronomical Society Vol.37 No.4

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.

CAN MASSIVE GRAVITY EXPLAIN THE MASS DISCREPANCY-ACCELERATION RELATION OF DISK GALAXIES?

Trippe, Sascha The Korean Astronomical Society 2013 Journal of The Korean Astronomical Society Vol.46 No.3

The empirical mass discrepancy-acceleration (MDA) relation of disk galaxies provides a key test for models of galactic dynamics. In terms of modified laws of gravity and/or inertia, the MDA relation quantifies the transition from Newtonian to modified dynamics at low centripetal accelerations $a_c{\lesssim}10^{-10}ms^{-2}$. As yet, neither dynamical models based on dark matter nor proposed modifications of the laws of gravity/inertia have predicted the functional form of the MDA relation. In this work, I revisit the MDA data and compare them to four different theoretical scaling laws. Three of these scaling laws are entirely empirical; the fourth one - the "simple ${\mu}$" function of Modified Newtonian Dynamics - derives from a toy model of gravity based on massive gravitons (the "graviton picture"). All theoretical MDA relations comprise one free parameter of the dimension of an acceleration, Milgrom's constant aM. I find that the "simple ${\mu}$" function provides a good fit to the data free of notable systematic residuals and provides the best fit among the four scaling laws tested. The best-fit value of Milgrom's constant is $a_M=(1.06{\pm}0.05){\times}10^{-10}ms^{-2}$. Given the successful prediction of the functional form of the MDA relation, plus an overall agreement with the observed kinematics of stellar systems spanning eight orders of magnitude in size and 14 orders of magnitude in mass, I conclude that the "graviton picture" is sufficient (albeit probably not a necessary nor unique approach) to describe galactic dynamics on all scales well beyond the scale of the solar system. This suggests that, at least on galactic scales, gravity behaves as if it was mediated by massive particles.

Signatures of minor mergers in the Milky Way disc – I. The SEGUE stellar sample

Gó,mez, Facundo A.,Minchev, Ivan,O’Shea, Brian W.,Lee, Young Sun,Beers, Timothy C.,An, Deokkeun,Bullock, James S.,Purcell, Chris W.,Villalobos, Á,lvaro Blackwell Publishing Ltd 2012 Monthly notices of the Royal Astronomical Society Vol.423 No.4

<P><B>ABSTRACT</B></P><P>It is now known that minor mergers are capable of creating structure in the phase‐space distribution of their host galaxy’s disc. In order to search for such imprints in the Milky Way, we analyse the Sloan Extension for Galactic Understanding and Exploration (SEGUE) F/G dwarf and the Schuster et al. stellar samples. We find similar features in these two completely independent stellar samples, consistent with the predictions of a Milky Way minor‐merger event. We next apply the same analyses to high‐resolution, idealized <I>N</I>‐body simulations of the interaction between the Sagittarius dwarf galaxy and the Milky Way. The energy distributions of stellar particle samples in small spatial regions in the host disc reveal strong variations of structure with position. We find good matches to the observations for models with a mass of Sagittarius’ dark matter halo progenitor <IMG src='/wiley-blackwell_img/lap.gif' alt ='less-than or approximately equal-to'/>10<SUP>11</SUP> M<SUB>⊙</SUB>. Thus, we show that this kind of analysis could be used to provide unprecedentedly tight constraints on Sagittarius’ orbital parameters, as well as place a lower limit on its mass.</P>