Первый релиз данных со спутника Gaia, благодаря большой временной базе (24 года) между наблюдениями Hipparcos и Gaia, позволил получить высокоточные собственные движения для примерно 2.5 млн звезд, которые опубликованы в каталоге TGAS (TGAS= Tycho-Gaia Astrometric Solution, описание метода см. Michalik et al . 2015). Мы использовали данные TGAS для изучения кинематики ОВ-ассоциаций, выделенных Блаха и Хамфрис (1989). Параметры кривой вращения, вычисленные с использованием собственных движений из каталогов TGAS и Hipparcos, согласуются в пределах ошибок. Среднее значение дисперсии скоростей звезд внутри 18 OB-ассоциаций, включающих не менее 10 звезд с собственными движениями из каталога TGAS, составляет 3.9 км/с, что заметно меньше, в 0.4 раза, чем аналогичная дисперсия скоростей, выведенная по собственным движениям из каталога Hipparcos. Знание дисперсии скоростей внутри ОВ-ассоциации позволяет нам оценить вириальную массу ее родительского гигантского молекулярного облака. Медианные значение вириальной и звездной масс ОВ-ассоциаций оказались равными $M_{vir} = 6.5 \cdot 10^5$ и $M_{st}=8.7 \cdot 10^3$ солнечных масс. Таким образом, ОВ-ассоциации должны быть несвязанными объектами, при условии, что они не содержат много плотного газа в своем объеме. Медианное значение эффективности звездообразования в ОВ-ассоциациях, равного отношению их звездной массы к массе газа в родительском облаке, составляет 1.8%, что согласуется с другими оценками. Минимальное значение приливного радиуса ОВ-ассоциаций, полученного в предположении, что масса ОВ-ассоциации определяется только массой ее звездной компоненты (M=M_st), имеет медиану 26 пк. Это означает, что, как минимум 61% звезд ОВ-ассоциаций находится внутри приливного радиуса. Мы обнаружили расширение ОВ-ассоциаций Per OB1, Cep OB2 и Car OB1, которое началось в малой области 25$\pm$5 пк 10$\pm$5 млн лет назад. Скорость расширения имеет среднее значение 5.4 км/c.
Bianca M. Poggianti, Alessia Moretti, Marco Gullieuszik, Jacopo Fritz, Yara Jaffe, Daniela Bettoni, Giovanni Fasano, Callum Bellhouse, George Hau, Benedetta Vulcani, Andrea Biviano, Alessandro Omizzolo, Angela Paccagnella, Mauro D'Onofrio, Antonio Cava, Y. -K. Sheen, Warrick Couch, Matt Owers
Published 2017-04-17, accepted for publication in ApJ
GASP (GAs Stripping Phenomena in galaxies with MUSE) is a new integral-fieldspectroscopic survey with MUSE at the VLT aiming at studying gas removalprocesses in galaxies. We present an overview of the survey and show a firstexample of a galaxy undergoing strong gas stripping. GASP is obtaining deepMUSE data for 114 galaxies at z=0.04-0.07 with stellar masses in the range10^9.2-10^11.5 M_sun in different environments (galaxy clusters and groups,over more than four orders of magnitude in halo mass). GASP targets galaxieswith optical signatures of unilateral debris or tails reminiscent of gasstripping processes ("jellyfish galaxies"), as well as a control sample of diskgalaxies with no morphological anomalies. GASP is the only existing IntegralField Unit (IFU) survey covering both the main galaxy body and the outskirtsand surroundings, where the IFU data can reveal the presence and the origin ofthe outer gas. To demonstrate GASP's ability to probe the physics of gas andstars, we show the complete analysis of a textbook case of a "jellyfish"galaxy, JO206. This is a massive galaxy (9 x 10^10 M_sun in a low-mass cluster(sigma ~500 km/s), at a small projected clustercentric radius and a highrelative velocity, with >=90kpc-long tentacles of ionized gas stripped away byram pressure. We present the spatially resolved kinematics and physicalproperties of gas and stars, and depict the evolutionary history of thisgalaxy.
C. Bellhouse, Y. L. Jaffe, G. K. T. Hau, S. L. McGee, B. M. Poggianti, A. Moretti, M. Gullieuszik, D. Bettoni, G. Fasano, M. D'Onofrio, J. Fritz, A. Omizzolo, Y. -K. Sheen, B. Vulcani
Published 2017-04-17, ApJ, revised version after referee comments, 15 pages, 16 figures. The interactive version of Figure 9 can be viewed at web.oapd.inaf.it/gasp/publications.html
This paper presents a spatially-resolved kinematic study of the jellyfishgalaxy JO201, one of the most spectacular cases of ram-pressure stripping (RPS)in the GASP (GAs Stripping Phenomena in Galaxies with MUSE) survey. By studyingthe environment of JO201, we find that it is moving through the denseintra-cluster medium of Abell 85 at supersonic speeds along our line of sight,and that it is likely accompanied by a small group of galaxies. Given thedensity of the intra-cluster medium and the galaxy's mass, projected positionand velocity within the cluster, we estimate that JO201 must so far have lost~50% of its gas during infall via RPS. The MUSE data indeed reveal a smoothstellar disk, accompanied by large projected tails of ionised (Halpha) gas,composed of kinematically cold (velocity dispersion <40km/s) star-forming knotsand very warm (>100km/s) diffuse emission which extend out to at least ~50 kpcfrom the galaxy centre. The ionised Halpha-emitting gas in the disk rotateswith the stars out to ~6 kpc but in the disk outskirts becomes increasinglyredshifted with respect to the (undisturbed) stellar disk. The observeddisturbances are consistent with the presence of gas trailing behind thestellar component, resulting from intense face-on RPS happening along the lineof sight. Our kinematic analysis is consistent with the estimated fraction oflost gas, and reveals that stripping of the disk happens outside-in, causingshock heating and gas compression in the stripped tails.
Jacopo Fritz, Alessia Moretti, Bianca Poggianti, Marco Gullieuszik, Gustavo Bruzual, Benedetta Vulcani, Fabrizio Nicastro, Yara Jaffe', Bernardo Cervantes Sodi, Daniela Bettoni, Giovanni Fasano, Stephane Charlot, Callum Bellhouse, George Hau
Published 2017-04-17, Submitted to ApJ, 22 pages, 15 figures
The so-called jellyfish galaxies are objects exhibiting disturbed morphology,mostly in the form of tails of gas stripped from the main body of the galaxy.Several works have strongly suggested ram pressure stripping to be themechanism driving this phenomenon. Here, we focus on one of these objects,drawn from a sample of optically selected jellyfish galaxies, and use it tovalidate sinopsis, the spectral fitting code that will be used for the analysisof the GASP (GAs Stripping Phenomena in galaxies with MUSE) survey, and studythe spatial distribution and physical properties of gas and stellar populationsin this galaxy. We compare the model spectra to those obtained with gandalf, acode with similar features widely used to interpret the kinematic of stars andgas in galaxies from IFU data. We find that sinopsis can reproduce thepixel-by-pixel spectra of this galaxy at least as good as gandalf does,providing reliable estimates of the underlying stellar absorption to properlycorrect the nebular gas emission. Using these results, we find strong evidencesof a double effect of ram pressure exerted by the intracluster medium onto thegas of the galaxy. A moderate burst of star formation, dating between 20 and500 Myr ago and involving the outer parts of the galaxy more strongly than theinner regions, was likely induced by a first interaction of the galaxy with theintracluster medium. Stripping by ram pressure, plus probable gas depletion dueto star formation, contributed to create a truncated ionized gas disk. Thepresence of an extended stellar tail on only one side of the disk, pointsinstead to another kind of process, likely a gravitational interaction by afly-by or a close encounter with another galaxy in the cluster.
Published 2017-04-18, 6 pages, 5 figures, accepted for publication in ApJL
Studies of cluster galaxies are increasingly finding galaxies withspectacular one-sided tails of gas and young stars, suggestive of intenseram-pressure stripping. These so-called "jellyfish" galaxies typically havelate-type morphology. In this paper, we present MUSE observations of anelliptical galaxy in Abell 2670 with long tails of material visible in theoptical spectra, as well as blobs with tadpole-like morphology. The spectra inthe central part of the galaxy reveals a stellar component as well as ionizedgas. The stellar component does not have significant rotation, while theionized gas defines a clear star-forming gas disk. We argue, based on deepoptical images of the galaxy, that the gas was most likely acquired during apast wet merger. It is possible that the star-forming blobs are also remnantsof the merger. In addition, the direction and kinematics of the one-sidedionized tails, combined with the tadpole morphology of the star-forming blobs,strongly suggests that the system is undergoing ram pressure from theintracluster medium. In summary, this paper presents the discovery of apost-merger elliptical galaxy undergoing ram pressure stripping.
Авторы исследуют ионизованный газ, выметенный из эллиптической(!) галактики в результате взаимодействия с межгалактической средой скопления Abell 2670. По-видимому, ионизованный газ в этой галактике был приобретен в результате слияния с богатым газом спутником (wet merger). Спектроскопия на MUSE позволяет четко видеть унаследованную кинематику выметенного из галактики газа.
Published 2017-04-17, TGAS selection-function code available at https://github.com/jobovy/gaia_tools, paper-specific code available at https://github.com/jobovy/tgas-completeness
The absolute number and the density profiles of different types of stars inthe solar neighborhood are a fundamental anchor for studies of the initial massfunction, stellar evolution, and galactic structure. Using data from the GaiaDR1 Tycho-Gaia Astrometric Solution, we reconstruct Gaia's selection functionand we determine Gaia's volume completeness, the local number density, and thevertical profiles of different spectral types along the main sequence fromearly A stars to late K stars as well as along the giant branch. We clearlydetect the expected flattening of the stellar density profile near themid-plane for all stellar types: All vertical profiles are well represented bysech^2 profiles, with scale heights ranging from ~50 pc for A stars to ~150 pcfor G and K dwarfs and giants. We determine the luminosity function along themain sequence for M_V < 7 (M >~ $0.72 M_\odot$) and along the giant branch forM_J >~ -2.5. Converting this to a mass function, we find that the high-mass (M> $1\,M_\odot$) present-day mass function along the main sequence is d n / d M= 0.016 $(M/M_\odot)^{-4.7}$ stars/pc^3/$M_\odot$. Extrapolating below M =$0.72\,M_\odot$, we find a total mid-plane stellar density of 0.040+/-0.002$M_\odot$/pc^3. Giants contribute 0.00039+/-0.00001 stars/pc^3 or about0.00046+/-0.00005 $M_\odot$/pc^3. The star-formation rate surface density is\Sigma(t) = 7+/-1 exp(-t/[7+/-1 Gyr]) $M_\odot$/pc^2/Gyr. Overall, we find thatGaia DR1's selection biases are manageable and allow a detailed new inventoryof the solar neighborhood to be made that agrees with and extends previousstudies. This bodes well for mapping the Milky Way with the full Gaia data set.
Первый заход на TGAS - подсчет звезд разных спектральных классов в цилиндре с основанием 50 пк и 200 пк. Вертикальное распределение - честный косеканс квадратный, со шкалой от 50 пк для молодых звезд до 150 пк для гигантов. Солнце лежит строго в экваториальной плоскости диска молодых звезд!
H. Akamatsu, Y. Fujita, T. Akahori, Y. Ishisaki, K. Hayashida, A. Hoshino, F. Mernier, K. Yoshikawa, K. Sato, J. S. Kaastra
Published 2017-04-19, 8 pages, 8 figures, accepted for publication in A&A
We report on the results of a $Suzaku$ observation of the plasma in thefilament located between the two massive clusters of galaxies Abell 399 andAbell 401. Abell 399 ($z$=0.0724) and Abell 401 ($z$=0.0737) are expected to bein the initial phase of a cluster merger. In the region between the twoclusters, we find a clear enhancement in the temperature of the filament plasmafrom 4 keV (expected value from a typical cluster temperature profile) to$kT\sim$6.5 keV. Our analysis also shows that filament plasma is present out toa radial distance of 15' (1.3 Mpc) from a line connecting the two clusters. Thetemperature profile is characterized by an almost flat radial shape with$kT\sim$6-7 keV within 10' or $\sim$0.8 Mpc. Across $r$=8'~from the axis, thetemperature of the filament plasma shows a drop from 6.3 keV to 5.1 keV,indicating the presence of a shock front. The Mach number based on thetemperature drop is estimated to be ${\cal M}\sim$1.3. We also successfullydetermined the abundance profile up to 15' (1.3 Mpc), showing an almostconstant value ($Z$=0.3 solar) at the cluster outskirt. We estimated theCompton $y$-parameter to be $\sim$14.5$\pm1.3\times10^{-6}$, which is inagreement with $Planck$'s results (14-17$\times10^{-6}$ on the filament). Theline of sight depth of the filament is $l\sim$1.1 Mpc, indicating that thegeometry of filament is likely a pancake shape rather than cylindrical. Thetotal mass of the filamentary structure is $\sim$7.7$\times10^{13}~\rmM_{\odot}$. We discuss a possible interpretation of the drop of X-ray emissionat the rim of the filament, which was pushed out by the merging activity andformed by the accretion flow induced by the gravitational force of thefilament.
Если по заголовку вы подумали, что речь идет о филаментах крупномасштабной структуры с газом первичного химсостава, то вы ошиблись. Это скорее приливной мост, соединяющий два сливающихся скопления галактик. И в рентгене авторы видят ударную волну от аккрецирующего на этот мост внешнего газа.
M. Kubo, T. Yamada, T. Ichikawa, M. Kajisawa, Y. Matsuda, I. Tanaka, H. Umehata
Published 2017-04-20, 18 pages, 14 figures, MNRAS accepted
We present the near-infrared high resolution imaging of an extremely densegroup of galaxies at the core of the protocluster at $z=3.09$ in the SSA22field by using the adaptive optics AO188 and the Infrared Camera andSpectrograph (IRCS) on Subaru Telescope. Wide morphological variety of themsuggests their on-going dramatic evolutions. One of the two quiescent galaxies(QGs), the most massive one in the group, is a compact elliptical with aneffective radius $r_{e} = 1.37\pm0.75$ kpc. It supports the two-phase formationscenario of giant ellipticals today that a massive compact elliptical is formedat once and evolves in the size and stellar mass by series of mergers. Sincethis object is a plausible progenitor of a brightest cluster galaxy (BCG) ofone of the most massive clusters today, it requires strong size ($\ga10$) andstellar mass ($\sim$ four times by $z=0$) growths. Another QG hosts an AGN(s)and is fitted with a model composed from an nuclear component and S\'ersicmodel. It shows spatially extended [O{\footnotesize III}]$\lambda$5007 emissionline compared to the continuum emission, a plausible evidence of outflows.Massive star forming galaxies (SFGs) in the group are two to three times largerthan the field SFGs at similar redshift. Although we obtained the $K$-bandimage deeper than the previous one, we found no candidate new members. Thisimplies a physical deficiency of low mass galaxies with stellar mass$M_{\star}\la4\times10^{10}~M_{\odot}$ and/or poor detection completeness ofthem owing to their diffuse morphologies.
Еще раз о предвзятой терминологии. В данном случае исследуется довольно большое, хотя и неоднородное по распределению объектов, скопление галактик на z=3. Только называть его скоплением LCDM не велит, поэтому это протоскопление. Исследуется центральная плотная часть. Две массивные галактики БЕЗ звездообразования - компактные, как им и положено. А вот 5 массивных галактик со звездообразованием - неожиданно протяженные. Авторы утешаются тем, что при такой плотной упаковке вся эта группа быстро сольется в одну галактику и не будет портить статистику на меньших красных смещениях.
We utilize the HSC CAMIRA cluster catalog and the photo-$z$ galaxy catalogconstructed in the HSC wide field (S16A), covering $\sim$ 174 deg$^{2}$, tostudy the star formation activity of galaxies in different environments over0.2 $<$ $z$ $<$ 1.1. We probe galaxies down to $i \sim$ 26, corresponding to astellar mass limit of log$_{10}$(M$_*$/M$_{\odot}$) $\sim$ 8.2 and $\sim$ 8.6for star-forming and quiescent populations, respectively, at $z$ $\sim$ 0.2.The existence of the red sequence for low stellar mass galaxies in clusterssuggests that the environmental quenching persists to halt the star formationin the low-mass regime. In addition, star-forming galaxies in groups orclusters are systematically biased toward lower values of specific starformation rate by 0.1 -- 0.3 dex with respect to those in the field and theoffsets shows no strong redshift evolution over our redshift range, implying auniversal slow quenching mechanism acting in the dense environments since $z$$\sim$ 1.1. Moreover, the environmental quenching dominates the mass quenchingin low mass galaxies, and the quenching dominance reverses in high mass ones.The transition mass is greater in clusters than in groups, indicating that theenvironmental quenching is more effective for massive galaxies in clusterscompared to groups.
Еще одно торжество японской технической мысли: несколько десятков тысяч галактик до z=1 отфотометрировано и разбито на поле, группы (10-25 членов) и скопления (более 25 членов). Искали, как водится, остановку звездообразования в галактиках при сборке скоплений на промежуточных красных смещениях. Как водится, не нашли: доля пассивных галактик среди массивных не зависит от окружения, а для маломассивных хотя и зависит, но не меняется с красным смещением.