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Star-forming Dwarf Galaxies: Internal motions and evolution
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Observational Astronomy.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The study of dwarf galaxies is important in order to better understand the physics of the young universe and how larger galaxies form and evolve. In this work we focus on Blue Compact Galaxies (BCGs) which havemuch enhanced star formation (starbursts), causing blue colours and strong emission line spectra.

Investigating of the inner motions of BCGs provides a means for determining masses and understanding what triggered the current starburst. We have used the Very Large Telescope to perform challenging observations of the stellar motions in several BCGs, as seen in the near-infrared Ca-triplet absorption lines. By comparing these to the kinematics of the ionized interstellar medium, we were able to look into the role of feeback from stellar winds and supernova explosions, as well as further strengthen the notion that the merging of galaxies plays an important role.

Spatially resolved spectroscopy can yield information about the 3D-structure of galaxies. We have used a Fabry-Perot interferometer to study the kinematics of the interstellar medium in two samples of galaxies, each containing about twenty objects. We find strong indications for ongoing galaxy mergers that correlate well with the strength of the star-formation activity. Furthermore, by estimating dynamical masses, BCGs are shown to be on average not dynamically supported by rotation.

In addition, we have used data from the Sloan Digital Sky Survey to study the frequency of starbursts in the local universe and the connection to their descendants. We selected starbursts by the strength of emission in H-alpha, the first Balmer recombination line, and post-starbursts by the strength of absorption in H-delta. These are indicators of currently ongoing and recent, on the order of 100 Myr, star-formation, respectively. By modelling the stellar populations we derive ages and masses and can establish a link between starbursts and postbursts in a time sequence. We find that starbursts are active on a 100 Myr timescale but are rare objects in the local universe.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , p. 27
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 977
Keywords [en]
Galaxy, Galaxies, Dynamics, Kinematics, Starburst, Dwarf Galaxies, Blue Compact Galaxies, Star Formation, Galaxy mergers, 3D-Spectroscopy, Spectroscopy
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
URN: urn:nbn:se:uu:diva-181481ISBN: 978-91-554-8483-5 (print)OAI: oai:DiVA.org:uu-181481DiVA, id: diva2:557091
Public defence
2012-11-12, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-10-19 Created: 2012-09-24 Last updated: 2013-01-23Bibliographically approved
List of papers
1. Star-gas decoupling and a non-rotating stellar core in He 2-10.: Integral field spectroscopy with FLAMES/ARGUS
Open this publication in new window or tab >>Star-gas decoupling and a non-rotating stellar core in He 2-10.: Integral field spectroscopy with FLAMES/ARGUS
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2007 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 474, no 1, p. 9-12Article in journal (Refereed) Published
Abstract [en]

Aims: We study the two-dimensional distribution and kinematics of the stellar and gaseous components in the centre of the blue compact dwarf galaxy He 2-10. The aim is to compare the kinematics of gas and stars in order to determine whether they are consistent with one another, or if stars and gas can be decoupled due to gravitational perturbations and feedback from star formation. Methods: We have used the integral field unit ARGUS, part of FLAMES on the European Southern Observatory's Very Large Telescope, to target the Ca ii λλ8498,8542,8662 Å triplet in the central 300 × 480 parsecs of He 2-10. The selected wavelength regime includes several prominent spectral features, including the Paschen series and the [S iii] emission-line, which we have used to derive the kinematics of the ionised interstellar medium. Results: We find no systematic trend in the velocities of the stars over the observed field of view and conclude that the stellar kinematics is governed by random motions. This is in contrast to the motions the ionised interstellar medium, where we find spatial velocity variations up to 60 km s-1. Our gas velocity field is consistent with previous studies of both the molecular gas and the feedback-driven outflow in He 2-10. We interpret the kinematic decoupling between the stars and the gas as He 2-10 being in the process of transformation to a dwarf elliptical galaxy.

Keywords
galaxies: dwarf, galaxies: kinematics and dynamics, galaxies: starburst, galaxies: individual: He 2-10
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-14414 (URN)10.1051/0004-6361:20078142 (DOI)
Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2017-12-11Bibliographically approved
2. Stellar dynamics of blue compact galaxies - II. Further indications of a merger in ESO 338-IG04
Open this publication in new window or tab >>Stellar dynamics of blue compact galaxies - II. Further indications of a merger in ESO 338-IG04
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2008 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 479, no 3, p. 725-733Article in journal (Refereed) Published
Abstract [en]

Context. Luminous blue compact galaxies, common at z similar to 1 but now relatively rare, show disturbed kinematics in emission lines. Aims. As part of a programme to understand their formation and evolution, we have investigated the stellar dynamics of a number of nearby objects in this class. Methods. We obtained long-slit spectra with VLT/FORS2 in the spectral region covering the near-infrared calcium triplet. In this paper we focus on the well-known luminous blue compact galaxy ESO338-IG04 (Tololo 1924 - 416). A previous investigation, using Fabry-Perot interferometry, showed that this galaxy has a chaotic Ha velocity field, indicating that either the galaxy is not in dynamical equilibrium or that Ha does not trace the gravitational potential due to feedback from star formation. Results. Along the apparent major axis, the stellar and ionised gas velocities for the most part follow each other. The chaotic velocity field must therefore be a sign that the young stellar population in ESO338-IG04 is not in dynamical equilibrium. The most likely explanation, which is also supported by its morphology, is that the galaxy has experienced a merger and that this has triggered the current starburst. Summarising the results of our programme so far, we note that emission-line velocity fields are not always reliable tracers of stellar motions, and go on to assess the implications for kinematic studies of similar galaxies at intermediate redshift.

Keywords
galaxies : evolution, galaxies : kinematics and dynamics, galaxies : individual : ESO338-IG04, galaxies : starburst, galaxies : interactions
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-112414 (URN)10.1051/0004-6361:20078916 (DOI)000253454600011 ()
Available from: 2010-01-14 Created: 2010-01-13 Last updated: 2017-12-12
3. Kinematics of Haro 11: a Luminous Blue Compact Galaxy, a Lyman Break Analogue and a micro Antennae
Open this publication in new window or tab >>Kinematics of Haro 11: a Luminous Blue Compact Galaxy, a Lyman Break Analogue and a micro Antennae
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(English)Manuscript (preprint) (Other academic)
Keywords
Galaxy, Galaxies, Dynamics, Kinematics, Starburst, Dwarf Galaxies, Blue Compact Galaxies, Star Formation, Galaxy mergers, 3D-Spectroscopy, Spectroscopy
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy with specialization in Astrophysics; Astronomy
Identifiers
urn:nbn:se:uu:diva-181473 (URN)
Available from: 2012-09-27 Created: 2012-09-24 Last updated: 2013-06-12
4. Kinematics of Blue Compact and a Volume-Limited Sample of HII Galaxies: A comparative study based on Fabry-Perot observations of the H-alpha line.
Open this publication in new window or tab >>Kinematics of Blue Compact and a Volume-Limited Sample of HII Galaxies: A comparative study based on Fabry-Perot observations of the H-alpha line.
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(English)Manuscript (preprint) (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-181562 (URN)
Available from: 2012-09-27 Created: 2012-09-26 Last updated: 2013-01-23
5. Local starburst galaxies and their descendants: Statistics from the Sloan Digital Sky Survey
Open this publication in new window or tab >>Local starburst galaxies and their descendants: Statistics from the Sloan Digital Sky Survey
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, article id A72Article in journal (Refereed) Published
Abstract [en]

Aims: Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies.

Methods: Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H alpha line. These masses agree excellently with the photometric masses. The mass (gas + stars) range is similar to 10(9)-10(11.5) M-circle dot. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/< SFR >, requiring that b >= 3. For postburst galaxies, we use, the equivalent width of H delta in absorption with the criterion EWH delta,abs >= 6 angstrom.

Results: We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3 6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages similar to 10 Myr, while almost no starbursts are found at ages >1 Gyr. The median baryonic burst mass fraction of sub-L* galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions >3%) is bimodal with a break at log M (M-circle dot) similar to 10.6, above which the ages are doubled. The starburst and postburst luminosity functions (LFs) follow each other closely until M-r similar to -21, when active galactic nuclei (AGNs) begin to dominate. The postburst LF continues to follow the AGN LF, while starbursts become less significant. This suggests that the number of luminous starbursts is underestimated by about one dex at high luminosities, because of having large amounts of dust and/or being outshone by an AGN. It also indicates that the starburst phase preceded the AGN phase. Finally, we look at the conditions for global gas outflow caused by stellar feedback and find that massive starburst galaxies are susceptible to such outflows.

National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-181565 (URN)10.1051/0004-6361/201525692 (DOI)000371589800083 ()
Funder
Swedish Research Council, 2011-5349Wenner-Gren FoundationsSwedish National Space Board
Available from: 2012-09-27 Created: 2012-09-26 Last updated: 2017-12-07Bibliographically approved

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