Understanding star formation rates (SFR) is a central goal of modernstar-formation models, which mainly involve gravity, turbulence and, in somecases, magnetic fields (B-fields). However, a connection between B-fields andSFR has never been observed. Here, a comparison between the surveys of SFR anda study of cloud-field alignment - which revealed a bimodal (parallel orperpendicular) alignment - shows consistently lower SFR per solar mass forclouds almost perpendicular to the B-fields. This is evidence of B-fields beinga primary regulator of SFR. The perpendicular alignment possesses asignificantly higher magnetic flux than the parallel alignment and thus astronger support of the gas against self-gravity. This results in overall lowermasses of the fragmented components, which are in agreement with the lower SFR.
Published 2017-06-22, Accepted for publication in MNRAS, 14 pages, 8 figures, 10 tables
We present the analysis of medium-resolution spectra obtained at the SouthernAfrican Large Telescope (SALT) for nuclear globular clusters (GCs) in two dwarfspheroidal galaxies (dSphs). The galaxies have similar star formationhistories, but they are situated in completely different environments.ESO269-66 is a close neighbour of the giant S0 NGC5128. KKs3 is one of the fewtruly isolated dSphs within 10 Mpc. We estimate the helium abundance $Y=0.3$,$\rm age=12.6\pm1$ Gyr, $[Fe/H]=-1.5,-1.55\pm0.2$ dex, and abundances of C, N,Mg, Ca, Ti, and Cr for the nuclei of ESO269-66 and KKs3. Our surface photometryresults using HST images yield the half-light radius of the cluster in KKs3,$\rm r_h=4.8\pm0.2$ pc. We demonstrate the similarities of medium-resolutionspectra, ages, chemical compositions, and structure for GCs in ESO269-66 andKKs3 and for several massive Galactic GCs with $[Fe/H]\sim-1.6$ dex. AllGalactic GCs posses Extended Blue Horizontal Branches and multiple stellarpopulations. Five of the selected Galactic objects are iron-complex GCs. Ourresults indicate that the sample GCs observed now in different environments hadsimilar conditions of their formation $\sim$1 Gyr after the Big Bang.
Published 2017-06-21, 32 pages, 10 figures, 7 tables; accepted for publication in MNRAS
We investigate the relation between the optical extinction ($A_V$) and thehydrogen column density ($N_H$) determined from X-ray observations of a largesample of Galactic sightlines toward 35 supernova remnants, 6 planetarynebulae, and 70 X-ray binaries for which $N_H$ was determined in the literaturewith solar abundances. We derive an average ratio of${N_H}/{A_V}=(2.08\pm0.02)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ for thewhole Galaxy. We find no correlation between ${N_H}/{A_V}$ and the numberdensity of hydrogen, the distance away from the Galactic centre, and thedistance above or below the Galactic plane. The ${N_H}/{A_V}$ ratio isgenerally invariant across the Galaxy, with${N_H}/{A_V}=(2.04\pm0.05)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ for the1st and 4th Galactic quadrants and ${N_H}/{A_V}=(2.09\pm0.03)\times10^{21}{\rmH\, cm^{-2}\, mag^{-1}}$ for the 2nd and 3rd Galactic quadrants. We alsoexplore the distribution of hydrogen in the Galaxy by enlarging our sample withadditional 74 supernova remnants for which both $N_H$ and distances are known.We find that, between the Galactic radius of 2 kpc to 10 kpc, the verticaldistribution of hydrogen can be roughly described by a Gaussian function with ascale height of $h=75.5\pm12.4\,{\rm pc}$ and a mid-plane density of$n_{H}(0)=1.11\pm0.15\,{\rm cm^{-3}}$, corresponding to a total gas surfacedensity of ${\sum}_{gas}{\sim}7.0\,{M_{\bigodot}}\,{\rm pc^{-2}}$. We alsocompile $N_H$ from 19 supernova remnants and 29 X-ray binaries for which $N_H$was determined with subsolar abundances. We obtain${N_H}/{A_V}=(2.47\pm0.04)\times10^{21}{\rm H\, cm^{-2}\, mag^{-1}}$ whichexceeds that derived with solar abundances by $\sim$20%. We suggest that infuture studies one may simply scale $N_H$ derived from subsolar abundances by afactor of $\sim$1.2 when converting to $N_H$ of solar abundances.
Sune Toft, Johannes Zabl, Johan Richard, Anna Gallazzi, Stefano Zibetti, Moire Prescott, Claudio Grillo, Allison W. S. Man, Nicholas Y. Lee, Carlos Gomez-Guijarro, Mikkel Stockmann, Georgios Magdis, Charles L. Steinhardt
Published 2017-06-21, Nature (June 22, 2017)
At redshift z = 2, when the Universe was just three billion years old, halfof the most massive galaxies were extremely compact and had already exhaustedtheir fuel for star formation(1-4). It is believed that they were formed inintense nuclear starbursts and that they ultimately grew into the most massivelocal elliptical galaxies seen today, through mergers with minorcompanions(5,6), but validating this picture requires higher-resolutionobservations of their centres than is currently possible. Magnification fromgravitational lensing offers an opportunity to resolve the inner regions ofgalaxies(7). Here we report an analysis of the stellar populations andkinematics of a lensed z = 2.1478 compact galaxy, which surprisingly turns outto be a fast-spinning, rotationally supported disk galaxy. Its stars must haveformed in a disk, rather than in a merger-driven nuclear starburst(8). Thegalaxy was probably fed by streams of cold gas, which were able to penetratethe hot halo gas until they were cut off by shock heating from the dark matterhalo(9). This result confirms previous indirect indications(10-13) that thefirst galaxies to cease star formation must have gone through major changes notjust in their structure, but also in their kinematics, to evolve intopresent-day elliptical galaxies.
R. M. González Delgado, E. Pérez, R. Cid Fernandes, R. García-Benito, R. López Fernández, N. Vale Asari, C. Cortijo-Ferrero, A. L. de Amorim, E. A. D. Lacerda, S. F. Sánchez, M. D. Lehnert, C. J. Walcher
Published 2017-06-19, 21 pages, 11 figures, 1 table, accepted for publication in Astronomy & Astrophysics, abstract abridged for arXiv submission
This paper presents the spatially resolved star formation history (SFH) ofnearby galaxies with the aim of furthering our understanding of the differentprocesses involved in the formation and evolution of galaxies. To this end, weapply the fossil record method of stellar population synthesis to a rich anddiverse data set of 436 galaxies observed with integral field spectroscopy inthe CALIFA survey. The sample covers a wide range of Hubble types, with stellarmasses ranging from $M_\star \sim 10^9$ to $7 \times 10^{11} M_\odot$. Spectralsynthesis techniques are applied to the datacubes to retrieve the spatiallyresolved time evolution of the star formation rate (SFR), its intensity($\Sigma_{\rm SFR}$), and other descriptors of the 2D-SFH in seven bins ofgalaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd), and five bins of stellarmass. Our main results are: a) Galaxies form very fast independently of theircurrent stellar mass, with the peak of star formation at high redshift ($z >2$). Subsequent star formation is driven by $M_\star$ and morphology, with lessmassive and later type spirals showing more prolonged periods of starformation. b) At any epoch in the past the SFR is proportional to $M_\star$,with most massive galaxies having the highest absolute (but lowest specific)SFRs. c) While nowadays $\Sigma_{\rm SFR}$ is similar for all spirals, andsignificantly lower in early type galaxies (ETG), in the past $\Sigma_{\rmSFR}$ scales well with morphology. The central regions of today's ETGs arewhere $\Sigma_{\rm SFR}$ reached the highest values ($> 10^3\,M_\odot\,$Gyr$^{-1}\,$pc$^{-2}$), similar to those measured in high redshiftstar forming galaxies. d) The evolution of $\Sigma_{\rm SFR}$ in Sbc systemsmatches that of models for Milky-Way-like galaxies, suggesting that theformation of a thick disk may be a common phase in spirals at early epochs.
V. Casasola, L. P. Cassara, S. Bianchi, S. Verstocken, E. Xilouris, L. Magrini, M. W. L. Smith, I. De Looze, M. Galametz, S. C. Madden, M. Baes, C. Clark, J. Davies, P. De Vis, R. Evans, J. Fritz, F. Galliano, A. P. Jones, A. V. Mosenkov, S. Viaene, N. Ysard
Published 2017-06-16, 33 pages, 9 figures (at low resolution here), 8 tables, Accepted for publication in A&A
The purpose of this work is the characterization of the radial distributionof dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18face-on spiral galaxies extracted from the DustPedia sample. This study isperformed by exploiting the multi-wavelength, from UV to sub-mm bands,DustPedia database, in addition to molecular (12CO) and atomic (HI) gas mapsand metallicity abundance information available in the literature. We fittedthe surface brightness profiles of the tracers of dust and stars, the masssurface density profiles of dust, stars, molecular gas, and total gas, and theSFR surface density profiles with an exponential curve and derived theirscale-lengths. We also developed a method to solve for the CO-to-H2 conversionfactor (alpha_CO) per galaxy by using dust and gas mass profiles. Although eachgalaxy has its own peculiar behaviour, we identified a common trend of theexponential scale-lengths vs. wavelength. On average, the scale-lengthsnormalized to the B-band 25 mag/arcsec^2 radius decrease from UV to 70 micron,from 0.4 to 0.2, and then increase back up to 0.3 at 500 microns. The mainresult is that, on average, the dust mass surface density scale-length is about1.8 times the stellar one derived from IRAC data and the 3.6 micron surfacebrightness, and close to that in the UV. We found a mild dependence of thescale-lengths on the Hubble stage T: the scale-lengths of the Herschel bandsand the 3.6 micron scale-length tend to increase from earlier to later types,the scale-length at 70 micron tends to be smaller than that at longer sub-mmwavelength with ratios between longer sub-mm wavelengths and 70 micron thatdecrease with increasing T. The scale-length ratio of SFR and stars shows aweak increasing trend towards later types.
Ioana Ciucă, Daisuke Kawata, Jane Lin, Luca Casagrande, George Seabroke, Mark Cropper
Published 2017-06-15, 9 pages, 7 figures, 1 table, submitted to MNRAS
We investigate the vertical metallicity gradients of five mono-age stellarpopulations between 0 and 11 Gyr for a sample of 18 435 dwarf stars selectedfrom the cross-matched Tycho-Gaia Astrometric Solution (TGAS) and RAdialVelocity Experiment (RAVE) Data Release 5. We find a correlation between thevertical metallicity gradients and age, with no vertical metallicity gradientin the youngest population and an increasingly steeper negative verticalmetallicity gradient for the older stellar populations. The metallicity at discplane remains almost constant between 2 and 8 Gyr, and it becomes significantlylower for the $8 < \tau \leqslant 11$ Gyr population. The current analysis alsoreveals that the intrinsic dispersion in metallicity increases steadily withage. We discuss that our results are consistent with a scenario that (thin)disc stars formed from a flaring (thin) star-forming disc.
We present the serendipitous discovery of an extended cold gas structureprojected close to the brightest cluster galaxy (BCG) of the z=0.045 clusterAbell 3716, from archival integral field spectroscopy. The gas is revealedthrough narrow Na D line absorption, seen against the stellar light of the BCG,which can be traced for $\sim$25 kpc, with a width of 2-4 kpc. The gas isoffset to higher velocity than the BCG (by $\sim$100 km/s), showing that it isinfalling rather than outflowing; the intrinsic linewidth is $\sim$80 km/s(FWHM). Very weak H$\alpha$ line emission is detected from the structure, and aweak dust absorption feature is suggested from optical imaging, but no stellarcounterpart has been identified. We discuss some possible interpretations forthe absorber: as a projected low-surface-brightness galaxy, as a stream of gasthat was stripped from an infalling cluster galaxy, or as a "retired" cool-corenebula filament.
В недалеком скоплении галактик Abell 3716 БЕЗ признаков охлаждающихся потоков в рентгене случайно, анализируя спектральный куб данных MUSE для центральной галактики (снятой в рамках обзора самых массивных галактик ближней Вселенной), заметили сбоку от галактики, частично в проекции на нее, линейный филамент, видимый в узкой абсорбции NaID. По скоростям - это натекание очень холодного газа НА галактику.
Published 2017-06-26, 11 pages, 6 figures, accepted in AJ
We investigate a sample of 3 dwarf elliptical galaxies in the Virgo Clusterwhich have significant reservoirs of HI. We present deep optical imaging (fromCFHT and KPNO), HI spectra (Arecibo) and resolved HI imaging (VLA) of thissample. These observations confirm their HI content and optical morphologies,and indicate that the gas is unlikely to be recently accreted. The sample hasmore in common with dwarf transitionals, although dwarf transitionals aregenerally lower in stellar mass and gas fraction. VCC 190 has an HI tidal tailfrom a recent encounter with the massive spiral galaxy NGC 4224. In VCC 611,blue star-forming features are observed which were unseen by shallower SDSSimaging.
В трех dE-галактиках скопления Virgo (из полной выборки 365) обнаружен нейтральный водород. Он не сильно влияет на морфологию и звездное население галактик; не показывает признаков вращения; судя по всему, является первичным, а не аккрецированным недавно.
Published 2017-06-28, 15 pages, 8 figures, comments welcome!
The number density of field galaxies per rotation velocity, referred to asthe velocity function, is an intriguing statistical measure probing thesmallest scales of structure formation. In this paper we point out that thevelocity function is sensitive to small shifts in key cosmological parameterssuch as the amplitude of primordial perturbations ($\sigma_8$) or the totalmatter density ($\Omega_{\rm m}$). Using current data and applying conservativeassumptions about baryonic effects, we show that the observed velocity functionof the Local Volume favours cosmologies in tension with the measurements fromPlanck but in agreement with the latest findings from weak lensing surveys.While the current systematics regarding the relation between observed and truerotation velocities are potentially important, upcoming data from HI surveys aswell as new insights from hydrodynamical simulations will dramatically improvethe situation in the near future.
Швейцарские космологи обратили внимание на работу Клыпина, Караченцева, Макарова и Насоновой 2015 года
о сильном недостатке крупных карликов в ближней Вселенной ПО ФУНКЦИИ РАСПРЕДЕЛЕНИЯ КРУГОВЫХ СКОРОСТЕЙ. Обсуждаются возможные модификации теоретических калибровок Vrot vs барионная масса. Показано, что НИ ПРИ КАКИХ идеях о подавлении барионного компонента карликовых галактик космологическая модель с параметрами, найденными недавно аппаратом Planck, не согласуются с наблюдаемой функцией скоростей.