13 research outputs found
The Lyman Alpha Reference Sample: V. The impact of neutral ISM kinematics and geometry on Lyman Alpha escape
We present high-resolution far-UV spectroscopy of the 14 galaxies of the
Lyman Alpha Reference Sample; a sample of strongly star-forming galaxies at low
redshifts (). We compare the derived properties to global
properties derived from multi band imaging and 21 cm HI interferometry and
single dish observations, as well as archival optical SDSS spectra. Besides the
Lyman line, the spectra contain a number of metal absorption features
allowing us to probe the kinematics of the neutral ISM and evaluate the optical
depth and and covering fraction of the neutral medium as a function of
line-of-sight velocity. Furthermore, we show how this, in combination with
precise determination of systemic velocity and good Ly spectra, can be
used to distinguish a model in which separate clumps together fully cover the
background source, from the "picket fence" model named by Heckman et al.
(2011). We find that no one single effect dominates in governing Ly
radiative transfer and escape. Ly escape in our sample coincides with a
maximum velocity-binned covering fraction of and bulk outflow
velocities of km s, although a number of galaxies show
these characteristics and yet little or no Ly escape. We find that
Ly peak velocities, where available, are not consistent with a strong
backscattered component, but rather with a simpler model of an intrinsic
emission line overlaid by a blueshifted absorption profile from the outflowing
wind. Finally, we find a strong anticorrelation between H equivalent
width and maximum velocity-binned covering factor, and propose a heuristic
explanatory model.Comment: 28 pages, 19 figures, 5 table
The Lyman Alpha Reference Sample: III. Properties of the Neutral ISM from GBT and VLA Observations
We present new H I imaging and spectroscopy of the 14 UV-selected
star-forming galaxies in the Lyman Alpha Reference Sample (LARS), aimed for a
detailed study of the processes governing the production, propagation, and
escape of Ly photons. New H I spectroscopy, obtained with the 100m
Green Bank Telescope (GBT), robustly detects the H I spectral line in 11 of the
14 observed LARS galaxies (although the profiles of two of the galaxies are
likely confused by other sources within the GBT beam); the three highest
redshift galaxies are not detected at our current sensitivity limits. The GBT
profiles are used to derive fundamental H I line properties of the LARS
galaxies. We also present new pilot H I spectral line imaging of 5 of the LARS
galaxies obtained with the Karl G. Jansky Very Large Array (VLA). This imaging
localizes the H I gas and provides a measurement of the total H I mass in each
galaxy. In one system, LARS 03 (UGC 8335 or Arp 238), VLA observations reveal
an enormous tidal structure that extends over 160 kpc from the main interacting
systems and that contains 10 M of H I. We compare various H I
properties with global Ly quantities derived from HST measurements. The
measurements of the Ly escape fraction are coupled with the new direct
measurements of H I mass and significantly disturbed H I velocities. Our
robustly detected sample reveals that both total H I mass and linewidth are
tentatively correlated with key Ly tracers. Further, on global scales,
these data support a complex coupling between Ly propagation and the H
I properties of the surrounding medium.Comment: Preprint form, 16 figures, accepted in Ap
The Lyman alpha reference sample. VII. Spatially resolved H kinematics
We present integral field spectroscopic observations with the Potsdam Multi
Aperture Spectrophotometer of all 14 galaxies in the Lyman Alpha
Reference Sample (LARS). We produce 2D line of sight velocity maps and velocity
dispersion maps from the Balmer (H) emission in our data
cubes. These maps trace the spectral and spatial properties of the LARS
galaxies' intrinsic Ly radiation field. We show our kinematic maps
spatially registered onto the Hubble Space Telescope H and Lyman
(Ly) images. Only for individual galaxies a causal connection
between spatially resolved H kinematics and Ly photometry can
be conjectured. However, no general trend can be established for the whole
sample. Furthermore, we compute non-parametric global kinematical statistics --
intrinsic velocity dispersion , shearing velocity ,
and the ratio -- from our kinematic maps. In
general LARS galaxies are characterised by high intrinsic velocity dispersions
(54\,km\,s median) and low shearing velocities (65\,km\,s
median). values range from 0.5 to 3.2 with an
average of 1.5. Noteworthy, five galaxies of the sample are dispersion
dominated systems with and are thus
kinematically similar to turbulent star forming galaxies seen at high redshift.
When linking our kinematical statistics to the global LARS Ly
properties, we find that dispersion dominated systems show higher Ly
equivalent widths and higher Ly escape fractions than systems with
. Our result indicates that turbulence in
actively star-forming systems is causally connected to interstellar medium
conditions that favour an escape of Ly radiation.Comment: 26 pages, 15 figures, accepted for publication in A&
CLusters in the Uv as EngineS (CLUES). II. Sub-kpc scale outflows driven by stellar feedback
We analyze the far-ultraviolet spectroscopy of 20 young and massive star
clusters (YSCs) in 11 nearby star-forming galaxies. We probe the interstellar
gas intervening along the line of sight, detecting several metal absorption
lines of a wide range of ionization potentials, from 6.0 eV to 77.5 eV.
Multiple-component Voigt fits to the absorption lines are used to study the
kinematics of the gas. We find that nearly all targets in the sample feature
gas outflowing from 30 up to 190 km per second, often both in the neutral and
ionized phase. The outflow velocities correlate with the underlying stellar
population properties directly linked to the feedback: the mass of the YSCs,
the photon production rate and the instantaneous mechanical luminosity produced
by stellar winds and SNe. We detect a neutral inflow in 4 targets, which we
interpret as likely not associated with the star cluster but tracing larger
scale gas kinematics. A comparison between the outflows energy and that
produced by the associated young stellar populations suggests an average
coupling efficiency of 10 per cent with a broad scatter. Our results extend the
relation found in previous works between galactic outflows and the host galaxy
star-formation rate to smaller scales, pointing towards the key role that
clustered star formation and feedback play in regulating galaxy growth.Comment: Accepted for publication on the Astronomical Journal on 14th February
2024. 32 pages, 13 figure
The Lyman alpha reference sample. II. Hubble space telescope imaging results, integrated properties, and trends
We report new results regarding the Lyα output of galaxies, derived from the Lyman Alpha Reference Sample, and focused on Hubble Space Telescope imaging. For 14 galaxies we present intensity images in Lyα, Hα, and UV, and maps of Hα/HÎČ, Lyα equivalent width (EW), and Lyα/Hα. We present Lyα and UV radial light profiles and show they are well-fitted by SĂ©rsic profiles, but Lyα profiles show indices systematically lower than those of the UV (n â 1-2 instead of gsim 4). This reveals a general lack of the central concentration in Lyα that is ubiquitous in the UV. Photometric growth curves increase more slowly for Lyα than the far ultraviolet, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii â10 kpc, suggesting that if placed at high-z only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total Lyα luminosities to be independent of all other quantities. Normalized Lyα throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and nebular quantities that suggest harder ionizing continuum and lower metallicity. Six galaxies would be selected as high-z Lyα emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Lyα and UV samples. A few galaxies have EWs above 50 Ă
, and one shows of 80%; such objects have not previously been reported at low-z
Ionized and atomic interstellar medium in star-forming galaxies
Star forming galaxies in the local Universe are an important laboratory for learning about conditions in the distant, early Universe. With a high frequency of interactions and mergers, strong star formation activity, and complex kinematics and often disturbed or irregular morphology, these galaxies are believed to be the best local analogs to the galaxies at early times, and can therefore help understand the galaxies we observe at high redshifts in the early Universe. These early galaxies in turn hold the key to cosmological insights about the early Universe, including galaxy formation and early evolution, the onset of the first stars, formation of the cosmic large scale structure, and the Epoch of Reionization. Many of these galaxies are primarily or only visible in the wavelengths of the Lyman α (Lyα) transition, corresponding to the energy shift in a transition from the first excited energy level to the ground state in atomic Hydrogen. However, Lyα radiation emitted from a galaxy interacts strongly with the neutral hydrogen in and around the galaxy, often transporting it over large distances before it is either absorbed by dust or escapes the galaxy far from the line of sight from its point of origin to Earth. Despite the intrinsic strength of the Lyα line, it is often completely absorbed or spread out over large projected areas of low surface density. The observed strength of Lyα is almost completely decoupled from the intrinsic strength and mainly regulated by the conditions in the gas it travels through. Therefore, to correctly interpret what we observe int Lyα at high redshifts, it is necessary to understand which processes regulate and which conditions facilitate its escape. Young starburst galaxies are also the main suspect for causing the reionization of the young Universe. To do so, the ionizing photons produced in the central starburst regions of the galaxies need to be able to reach the intergalactic gas. Like Lyα, the ionizing radiation (the Lyman Continuum) also interacts with the neutral medium. While not as strongly as for Lyα, it is still strong enough that at the onset of this project, only two galaxies in the local Universe were confirmed Lyman Continuum leakers. Since then, another few handful local candidates and confirmed leakers have been announced, but still far from the escape fractions needed at high redshift to reionize the early Universe. Identifying which properties of the ISM govern Lyman Continuum escape, and how these evolve with redshift, is a hot topic in extragalactic astronomy these years. This thesis consists of projects which, in each their way, aim to deepen our understanding of these matters. One project, the Lyman Alpha Reference Sample (LARS), aims to understand which processes govern Lyα radiative transfer through careful, in-depth studies of a sample of 14 local starburst galaxies with a selection of powerful telescopes and instruments. My contribution to this was a spectroscopic analysis of the central star-forming regions to understand their physical properties (Paper I), and of neutral Hydrogen interstellar and circumgalactic systems which interact with Lyα radiation on its way out of the galaxies (Paper II). In Paper III, I performed a deeper, more detailed spectroscopic analysis of the central recombination regions in two local-universe starburst galaxies, of which one is a known Lyman Continuum leaker. Finally, in Papers IV and V, we shift focus focus somewhat to combine information in Lyα and Lyman Continuum (and, in the case of Paper IV, other auxiliary data) from observations of the two first known Lyman Continuum leakers, to understand which configurations of neutral gas would allow for the combination of Lyman Continuum leakage and Lyα spectral and physical morphology that is observed.Aktivt stjÀrnbildande galaxer Àr en viktig och vÀrdefull kÀlla till kunskap om förhÄllanden i det unga, avlÀgsna universum. Med en hög frekvens av interaktioner och krockar, stark stjÀrnbildningsaktivitet, komplicerad kinematik och ofta rubbade eller helt oregelbundna former, Àr det en vanlig uppfattning bland astronomer att dessa galaxer Àr det nÀrmaste vi kommer en lokal analog till galaxerna i universums barndom. De Àr dÀrför mycket vÀrdefulla som nyckel till att förstÄ vad vi ser nÀr vi observerar unga galaxer vid hög rödförskjutning i det unga universum. Dessa unga galaxer i sin tur Àr viktiga nycklar till kosmologisk insikt om universums tidigaste epoker, t.ex. de första stjÀrnornas uppkomst, hur universums storskaliga struktur bildats, och det tidiga universums Äterjonisering. MÄnga av dessa tidiga, avlÀgsna galaxern Àr primÀrt eller uteslutande synliga i vÄglÀngdsomrÄdet runt den sÄ kallade Lyman α (Lyα) linjen; vÄglÀngden motsvarande energin i övergÄngen frÄn första exciterade energinivÄn till grundnivÄn i en neutral vÀteatom. Lyα-strÄlning utsÀnds frÄn de centrala delarna av en galax och vÀxelverkar starkt med neutrala vÀtemoln i och omkring galaxen. Ofta transporteras en Lyα-foton genom talrika vÀxelverkningar lÄng bort frÄn sin ursprungspunkt innan den antingen absorberas av stoftpartiklar eller slipper ut ur galaxen till den intergalaktiska rymden. Trots Lyα-linjens ursprungliga styrka absorberas den ofta totalt, eller sprids ut över stora projicerade arealer med relativt lÄg ytdensitet. Den ljusstyrka som observeras i Lyα Àr statistiskt nÀstan fullstÀndigt frÄnkopplad frÄn den ursprungliga styrkan och regleras i huvudsak av fysiska förhÄllanden i gasen, som strÄlningen passerar genom. För att kunna tolka observationer av Lyα vid hög rödförskjutning rÀtt Àr det dÀrför viktigt att förstÄ, vilka processer som reglerar, och vilka förhÄllanden som tillÄter, att strÄlningen slipper ut ur galaxen. Unga, sÄ kallade Starburst-galaxer anses Àven vara den mest sannolika huvudorsaken till Äterjoniseringen av det unga universum. För att kunna göra detta mÄste de joniserande UV-fotonerna (i det sÄ kallade Lyman Continuum), som produceras i de centrala starburst-regionerna av dessa galaxer, lyckas slippa igenom galaxens mÄnga och ofta tjocka vÀtemoln och ut ur galaxen. Precis som med Lyα, interagerar Àven dessa Lyman Continuum-fotoner med neutrala vÀtemoln, fast inte lika starkt som Lyα. Dock Àr det tillrÀckligt starkt för att astronomer, nÀr detta projekt pÄbörjades, ba- ra skulle kÀnna till tvÄ galaxer som utstrÄlar mÀtbara mÀngder Lyman Continuum-strÄlning. Sedan dess har det hittats ett tiotals kandidater och bekrÀftade fall dÀr Lyman Continuum-fotoner observerats frÄn lokala galaxer, men fortfarande lÄngt ifrÄn tillrÀckligt med joniserande strÄlning för att Äterjonisera det unga universum. Astronomer arbetar dÀrför med att identifiera vilka egenskaper hos det interstellara mediet som reglerar Lyman Continuum-utstrÄlning, och hur dessa utvecklar sig med rördförskjutning över kosmologisk tid. Denna avhandling bestÄr av projekt som, var pÄ sitt sÀtt, syftar till att förbÀttra vÄr förstÄelse av dessa frÄgor. Det första projektet, LARS, har som mÄlsÀttning att förstÄ vilka processer som reglerar Lyα-strÄlningstransport genom fördjupade studier av 14 lokala, stjÀrnbildande galaxer med en rad av kraftfulla teleskop och instrument. Mitt bidrag var spektroskopisk analys av de centrala stjÀrnbildande regionerna för att förstÄ dessa regioners fysiska egenskaper (Artikel I); och av neutrala vÀtemolnen genom vilka Lyα-strÄlningen mÄste transporteras för att nÄ fram till vÄra teleskop (Artikel II). I Artikel III företar vi Ànnu djupare, mer detaljerade spektroskopiska studier av de heta centrala, högt joniserade regionerna i tvÄ lokala, stjÀrnbildande galaxer. I Artikel IV och V flyttas fokus till att kombinera den tillgÀngliga informationen om Lyα och Lyman Continuum-strÄlning i de tvÄ första kÀnda Lyman Continuum-utstrÄlande galaxerna för att förstÄ vilka konfigurationer av det interstellara mediet som kan föranleda utstrÄlning av joniserande fotoner och Lyα i den utformning det observeras.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 4: Submitted. Paper 5: Manuscript.</p
Slicing the cool circumgalactic medium along the major axis of a star-forming galaxy at z = 0.7
We present spatially resolved Echelle spectroscopy of an intervening MgâIIâFeâIIâMgâI absorption-line system detected at zabs = 0.73379 towards the giant gravitational arc PSZ1 G311.65â18.48. The absorbing gas is associated with an inclined disc-like star-forming galaxy, whose major axis is aligned with the two arc-segments reported here. We probe in absorption the galaxyâs extended disc continuously, at â3âkpc sampling, from its inner region out to 15Ă the optical radius. We detect strong (â W27960>0.3Ă
) coherent absorption along 13 independent positions at impact parameters D = 0â29âkpc on one side of the galaxy, and no absorption at D = 28â57âkpc on the opposite side (all de-lensed distances at zabs). We show that (1) the gas distribution is anisotropic; (2) W27960â , W26000â , W28520â , and the ratio W26000/W27960â , all anticorrelate with D; (3) the W27960âD relation is not cuspy and exhibits significantly less scatter than the quasar-absorber statistics; (4) the absorbing gas is co-rotating with the galaxy out to D âČ 20âkpc, resembling a âflatâ rotation curve, but at D âł 20âkpc velocities decline below the expectations from a 3D disc-model extrapolated from the nebular [OâII] emission. These signatures constitute unambiguous evidence for rotating extra-planar diffuse gas, possibly also undergoing enriched accretion at its edge. Arguably, we are witnessing some of the long-sought processes of the baryon cycle in a single distant galaxy expected to be representative of such phenomena
CLusters in the Uv as EngineS (CLUES). II. Subkiloparsec-scale Outflows Driven by Stellar Feedback
We analyze the far-ultraviolet (1130â1770 Ă
rest frame) spectroscopy of 20 young (10 ^4 M _â ) star clusters (YSCs) in 11 nearby star-forming galaxies. We probe the interstellar gas intervening along the line of sight, detecting several metal absorption lines of a wide range of ionization potentials, from 6.0 to 77.5 eV. Multiple-component Voigt fits to the absorption lines are used to study the kinematics of the gas. We find that nearly all targets in the sample feature gas outflowing from 30 up to 190 km s ^â1 , often in both the neutral and ionized phases. The outflow velocities correlate with the underlying stellar population properties directly linked to the feedback: the mass of the YSCs, the photon production rate, and the instantaneous mechanical luminosity produced by stellar winds and supernovae. We detect a neutral inflow in four targets, which we interpret as likely not associated with the star cluster but tracing larger-scale gas kinematics. A comparison between the outflowsâ energy and that produced by the associated young stellar populations suggests an average coupling efficiency of 10% with a broad scatter. Our results extend the relation found in previous works between galactic outflows and the host galaxy star formation rate to smaller scales, pointing toward the key role that clustered star formation and feedback play in regulating galaxy growth