| 1. |
- Calzetti, D., et al.
(författare)
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Spatially Resolved Dust, Gas, and Star Formation in the Dwarf Magellanic Irregular NGC 4449
- 2018
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 852:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the relation between gas and star formation in subgalactic regions, similar to 360. pc to similar to 1.5. kpc in size, within the nearby starburst dwarf NGC 4449, in order to separate the underlying relation from the effects of sampling at varying spatial scales. Dust and gas mass surface densities are derived by combining new observations at 1.1. mm, obtained with the AzTEC instrument on the Large Millimeter Telescope, with archival infrared images in the range 8-500 mu m from the Spitzer Space Telescope and the Herschel Space Observatory. We extend the dynamic range of our millimeter (and dust) maps at the faint end, using a correlation between the far-infrared/millimeter colors F(70)/F(1100) (and F(160)/F(1100)) and the mid-infrared color F(8)/F(24) that we establish for the first time for this and other galaxies. Supplementing our data with maps of the extinction-corrected star formation rate (SFR) surface density, we measure both the SFR-molecular gas and the SFR-total. gas relations in NGC 4449. We find that the SFR-molecular. gas relation is described by a power law with an exponent that decreases from similar to 1.5 to similar to 1.2 for increasing region size, while the exponent of the SFR-total. gas relation remains constant with a value of similar to 1.5 independent of region size. We attribute the molecular law behavior to the increasingly better sampling of the molecular cloud mass function at larger region sizes; conversely, the total gas law behavior likely results from the balance between the atomic and molecular gas phases achieved in regions of active star formation. Our results indicate a nonlinear relation between SFR and gas surface density in NGC 4449, similar to what is observed for galaxy samples.
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| 2. |
- Guaita, Lucia, et al.
(författare)
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The Lyman alpha reference sample IV. Morphology at low and high redshift
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 576
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Tidskriftsartikel (refereegranskat)abstract
- Context. The transport of Ly alpha photons in galaxies is a complex process and the conditions under which Ly alpha photons manage to escape from certain galaxies is still under investigation. The Lyman alpha reference sample (LARS) is a sample of 14 local star-forming galaxies, designed to study Ly alpha in detail and relate it to rest-frame UV and optical emission. Aims. With the aim of identifying rest-frame UV and optical properties, which are typical of Ly alpha emitters (LAEs, galaxies with EW(Ly alpha) > 20 angstrom) at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Ly alpha radiation. Methods. We measured sizes and morphological parameters in the continuum, Ly alpha, and Ha images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. We then simulated LARS galaxies at z similar to 2 and 5.7, performing the same morphological measurements. We also investigated the detectability of LARS galaxies in current deep field observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to provide a comparison to stacking studies performed at high redshift. Results. LARS galaxies have continuum size, stellar mass, and rest-frame absolute magnitude typical of Lyman break analogues in the local Universe and also similar to 2 < z < 3 star-forming galaxies and massive LAEs. LARS optical morphology is consistent with the one of merging systems, and irregular or starburst galaxies. For the first time we quantify the morphology in Ly alpha images: even if a variety of intrinsic conditions of the interstellar medium can favour the escape of Ly alpha photons, LARS-LAEs appear small in the continuum, and their Ly alpha is compact. LARS galaxies tend to be more extended in Ly alpha than in the rest-frame UV. It means that Ly alpha photons escape by forming haloes around HII regions of LARS galaxies. Conclusions. The stack of LARS-LAE Ly alpha images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended. This can be caused by the variety of dust and HI amount and distribution, which produces a more complex, patchy, and extended profile, like the one observed for Lyman break galaxies that can contribute to the stack. We cannot identify a single morphological property that controls whether a galaxy emits a net positive Ly alpha flux. However, the LARS-LAEs have continuum properties consistent with merging systems.
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| 3. |
- Herenz, Edmund Christian, et al.
(författare)
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The Lyman alpha reference sample VII. Spatially resolved H alpha kinematics
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 587
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Tidskriftsartikel (refereegranskat)abstract
- We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z similar to 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer alpha (H alpha) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Ly alpha radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope H alpha and Lyman alpha (Ly alpha) images. We can conjecture a causal connection between spatially resolved H alpha kinematics and Ly alpha photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion sigma(0), the shearing velocity v(shear), and the v(shear)/sigma(0) ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s(-1) median) and low shearing velocities (65 km s(-1) median). The v(shear/sigma 0) values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v(shear)/sigma(0) < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Ly alpha properties, we find that dispersion-dominated systems show higher Ly alpha equivalent widths and higher Ly alpha escape fractions than systems with v(shear)/sigma(0) > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Ly alpha radiation.
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| 4. |
- Le Reste, Alexandra, 1995-, et al.
(författare)
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LARS XIII : High Angular Resolution 21 cm H ı Observations of Lyα Emitting Galaxies
- 2022
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 934:1
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Tidskriftsartikel (refereegranskat)abstract
- The Lyα emission line is one of the main observables of galaxies at high redshift, but its output depends strongly on the neutral gas distribution and kinematics around the star-forming regions where UV photons are produced. We present observations of Lyα and 21 cm H ı emission at comparable scales with the goal to qualitatively investigate how the neutral interstellar medium (ISM) properties impact Lyα transfer in galaxies. We have observed 21 cm H ı at the highest possible angular resolution (≈3'' beam) with the Very Large Array in two local galaxies from the Lyman Alpha Reference Sample. We compare these data with Hubble Space Telescope Lyα imaging and spectroscopy, and Multi Unit Spectroscopic Explorer and Potsdam MultiAperture Spectrophotometer ionized gas observations. In LARS08, high-intensity Lyα emission is cospatial with high column density H ı where the dust content is the lowest. The Lyα line is strongly redshifted, consistent with a velocity redistribution that allows Lyα escape from a high column density neutral medium with a low dust content. In eLARS01, high-intensity Lyα emission is located in regions of low column density H ı, below the H ı data sensitivity limit ( < 2 × 1020 cm−2). The perturbed ISM distribution with low column density gas in front of the Lyα emission region plays an important role in the escape. In both galaxies, the faint Lyα emission (∼1×10−16 erg s−1cm−2 arcsec−2) traces intermediate Hα emission regions where H ı is found, regardless of the dust content. Dust seems to modulate, but not prevent, the formation of a faint Lyα halo. This study suggests the existence of scaling relations between dust, Hα, H ı, and Lyα emission in galaxies.
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| 5. |
- Melinder, Jens, et al.
(författare)
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Lyman alpha escape from 45 star forming galaxies– the Lyα Reference Sample XIV
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present Lyα imaging of 45 low redshift star-forming galaxies observed with the Hubble space telescope. The galaxies have been selected to have moderate to high star formation rates using FUVluminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity have been applied. We employ a pixel SED fitting code to obtain accurate continuum subtracted Lyα, Hα and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction ofLyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anti-correlated with both nebular and stellar extinction, weakly anti-correlated with stellar mass, but no conclusive evidence for correlations to other quantities. We show that Lyα escape fractions are inconsistent with common dust extinction laws and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present a star formation rate calibration based on Lyαluminosity, where the equivalent width of Lyα is used to correct for non-unity escape fraction, and show that this relation provides a reasonably accurate calibration but with a large scatter. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius
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| 6. |
- Melinder, Jens, 1977-, et al.
(författare)
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The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission
- 2023
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Ingår i: Astrophysical Journal Supplement Series. - 0067-0049 .- 1538-4365. ; 266:1
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Tidskriftsartikel (refereegranskat)abstract
- We present Lyα imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates (SFRs) using far-ultraviolet (FUV) luminosity and Hα equivalent width criteria, but no constraints on Lyα luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Lyα, Hα, and Hβ maps. We find that Lyα is less concentrated than FUV and optical line emission in almost all galaxies with significant Lyα emission. We present global measurements of Lyα and other quantities measured in apertures designed to capture all of the Lyα emission. We then show how the escape fraction of Lyα relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Lyα escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present an SFR calibration based on Lyα luminosity, where the equivalent width of Lyα is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Lyα for the galaxies that can be used to find aperture loss fractions at a given physical radius.
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| 7. |
- Pardy, Stephen A., et al.
(författare)
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THE LYMAN ALPHA REFERENCE SAMPLE. III. PROPERTIES OF THE NEUTRAL ISM FROM GBT AND VLA OBSERVATIONS
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 794:2
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Tidskriftsartikel (refereegranskat)abstract
- We present new Hi 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 alpha photons. New Hi spectroscopy, obtained with the 100 m Green Bank Telescope (GBT), robustly detects the Hi 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 Hi line properties of the LARS galaxies. We also present new pilot Hi spectral line imaging of five of the LARS galaxies obtained with the Karl G. Jansky Very Large Array (VLA). This imaging localizes the Hi gas and provides a measurement of the total Hi 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(9) M-circle dot of Hi. We compare various Hi properties with global Ly alpha quantities derived from Hubble Space Telescope measurements. The measurements of the Ly alpha escape fraction are coupled with the new direct measurements of Hi mass and significantly disturbed Hi velocities. Our robustly detected sample reveals tentative correlations between the total Hi mass and linewidth, and key Ly alpha tracers. Further, on global scales, these data support a complex coupling between Ly alpha propagation and the Hi properties of the surrounding medium.
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| 8. |
- Puschnig, Johannes, et al.
(författare)
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Correcting sky-quality-meter measurements for ageing effects using twilight as calibrator
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 502:1, s. 1095-1103
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Tidskriftsartikel (refereegranskat)abstract
- In the last decade, numerous sky quality meters (SQMs) have been installed around the world, aiming to assess the temporal change of the night sky brightness, and thus the change in light pollution. However, it has become clear that SQM readings may be affected by ageing effects such as degradation of the sensor sensitivity and/or loss of transmissivity of optical components (filter, housing window). To date, the magnitude of the darkening has not been assessed in a systematic way. We report for the first time on the quantification of the SQM ageing effect and describe the applied method. We combine long-term SQM measurements obtained between 2011 and 2019 in Potsdam-Babelsberg (23 km to the south-west of the centre of Berlin), Vienna and Stockholm with a readily available empirical twilight model, which serves as a calibrator. Twilight SQM observations, calibrated for changing Sun altitudes, reveal a linear degradation of the measurement systems (SQM + housing window) with the following slopes: 34 +/- 4, 46 +/- 2 and 53 +/- 2 mmag(SQM) arcsec(-2) yr(-1) for Stockholm, Potsdam-Babelsberg and Vienna, respectively. With the highest slope found in Vienna (latitude similar to 48 degrees) and the lowest one found in Stockholm (latitude similar to 59 degrees), we find an indication for the dependence of the trend on solar irradiance (which is a function of geographic latitude).
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| 9. |
- Puschnig, Johannes, 1980-
(författare)
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How ISM properties drive Lyman Continuum Escape
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis introduces physical processes that are at work in astrophysical plasmas and reviews the current state of research related to the emission of ionizing photons, i.e. Lyman continuum (LyC). Star forming galaxies and active galactic nuclei are discussed as sources of LyC. Observations of LyC leakage at all redshifts are summarized and escape fractions are brought into a cosmological context, i.e. its implications for the reionization of the Universe, one of the major gas phase changes that was completed already after ∼1Gyr after the Big Bang at redshift z∼6.The main work focuses on observations of the local LyC leaking galaxy Tololo 1247-232. Physical properties of the interstellar medium, its porosity and neutral medium column density, could be derived using newly obtained Hubble Space Telescope (HST) data. The work is based on spectroscopy obtained with the Cosmic Origins Spectrograph (COS), as well as optical and ultraviolet multi-band imaging with the Wide Field Camera 3 (WFC3). An improved COS data reduction procedure was adopted. The recent detection of ionizing radiation emerging from Tololo 1247-232 could be confirmed. A LyC escape fraction of 6.6% was derived, in agreement with previous results. We used FUV absorption lines of Si II and Si IV as a probe of the neutral and ionized interstellar medium and find that most of the ISM gas is ionized, likely facilitating LyC escape from density bounded regions. Neutral gas covering as a function of line-of-sight velocity is derived using the apparent optical depth method. The ISM is found to be sufficiently clumpy, supporting the direct escape of LyC photons. We further report on broadband UV and optical continuum imaging as well as narrowband imaging of Lyα, Hα and Hβ. We also performed VLA 21cm imaging. The hydrogen hyperfine transition was not detected, but a deep upper limit atomic gas mass of 10^9 Mo could be derived. The upper limit gas fraction is only 20 percent. Evidence is found that the H I gas halo is relatively small compared to other Lyman Alpha emitters.
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| 10. |
- Puschnig, Johannes, et al.
(författare)
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Long-term trends of light pollution assessed from SQM measurements and an empirical atmospheric model(dagger)
- 2022
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 518:3, s. 4449-4465
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Tidskriftsartikel (refereegranskat)abstract
- We present long-term (4–10 yr) trends of light pollution observed at 26 locations, covering rural, intermediate, and urban sites, including the three major European metropolitan areas of Stockholm, Berlin, and Vienna. Our analysis is based on (i) night sky brightness (NSB) measurements obtained with sky quality metres (SQMs) and (ii) a rich set of atmospheric data products. We describe the SQM data reduction routine in which we filter for moon- and clear-sky data and correct for the SQM ‘aging’ effect using an updated version of the twilight method of Puschnig et al. (2021). Our clear-sky, aging-corrected data reveal short- and long-term (seasonal) variations due to atmospheric changes. To assess long-term anthropogenic NSB trends, we establish an empirical atmospheric model via multivariate penalized linear regression. Our modelling approach allows to quantitatively investigate the importance of different atmospheric parameters, revealing that surface albedo and vegetation have by far the largest impact on zenithal NSB. Additionally, the NSB is sensitive to black carbon and organic matter aerosols at urban and rural sites, respectively. Snow depth was found to be important for some sites, while the total column of ozone leaves impact on some rural places. The average increase in light pollution at our 11 rural sites is 1.7 per cent per year. At our nine urban sites, we measure an increase of 1.8 per cent per year and for the remaining six intermediate sites we find an average increase of 3.7 per cent per year. These numbers correspond to doubling times of 41, 39, and 19 yr. We estimate that our method is capable of detecting trend slopes shallower/steeper than ±1.5 per cent per year.
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