Ultraviolet Morphology and Star Formation in the Tidal Tails of NGC 4038/39 (original) (raw)
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The Astrophysical Journal, 2005
New GALEX observations have detected significant FUV (1530Å) and NUV (2310Å) emission from stellar substructures within the tidal tails of four ongoing galaxy mergers. The UV-bright regions are optically faint and are coincident with HI density enhancements. FUV emission is detected at any location where the HI surface density exceeds ∼ 2 M ⊙ pc −2 , and is often detected in the absence of visible wavelength emission. UV luminosities of the brighter regions of the tidal tails imply masses of 10 6 M ⊙ up to ∼ 10 9 M ⊙ in young stars in the tails, and HI luminosities imply similar HI masses. UV-optical colors of the tidal tails indicate stellar populations as young as a few Myr, and in all cases ages < 400Myr. Most of the young stars in the tails formed in single bursts rather than resulting from continuous star formation, and they formed in situ as the tails evolved. Star -2formation appears to be older near the parent galaxies and younger at increasing distances from the parent galaxy. This could be because the star formation occurs progressively along the tails, or because the star formation has been inhibited near the galaxy/tail interface. The youngest stellar concentrations, usually near the ends of long tidal tails, have masses comparable to confirmed tidal dwarf galaxies and may be newly forming galaxies undergoing their first burst of star formation. a NUV−R for Arp 295, or NUV−V for NGC 520, as indicated by †.
GALEX Ultraviolet Observations of the Interacting Galaxy NGC 4438 in the Virgo Cluster
The Astrophysical Journal, 2005
We present GALEX NUV (2310Å) and FUV (1530Å) images of the interacting galaxy NGC 4438 (Arp 120) in the center of the Virgo cluster. These images show an extended (20 kpc) tidal tail at the north-west edge of the galaxy previously undetected at other wavelengths, at 15-25 kpc from its nucleus. Except in the nucleus, the UV morphology of NGC 4438 is totally different from the Hα+ [NII] one, more similar to the X-ray emission, confirming its gas cooling origin. We study the star formation history of NGC 4438 combining spectro-photometric data in the UV-visible-near-IR wavelength range with population synthesis and galaxy evolution models. The data are consistent with a recent (∼ 10 Myr), instantaneous burst of star formation in the newly discovered UV north-western tail which is significantly younger than the age of the tidal interaction with NGC 4435, dated by dynamical models at ∼ 100 Myr ago. Recent star formation events are also present at the edge of the northern arm and in the southern tail, while totally lacking in the other regions, which are dominated by the old stellar population perturbed during the dynamical interaction with NGC 4435. The contribution of this recent starburst to the total galaxy stellar mass is lower than 0.1%, an extremely low value for such a violent interaction. High-velocity, off-center tidal encounters such as that observed in Arp 120 are thus not sufficient to significantly increase the star formation activity of cluster galaxies.
The Astrophysical Journal, 1998
The bright Magellanic irregular galaxy NGC 4449 was observed during the Astro-2 Space Shuttle mission by the Ultraviolet Imaging Telescope (UIT), which obtained images of a 40@ Ðeld centered on the galaxy in two broad far-ultraviolet (FUV) bands centered at 1520 and 1620 with 3AÈ5A spatial A , resolution. Together with Ha and Hb Ñuxes from ground-based Fabry-Perot images, these data are analyzed in order to explore the recent star formation history of NGC 4449. Maps of the Ha-to-FUV and FUVÈtoÈblue continuum Ñux ratios are presented and interpreted using evolutionary synthesis models. Photometry is presented both for 22 apertures containing large OB complexes and for 57 small apertures containing compact FUV-emitting knots. The OB complexes along the northern edge of the visible system have high Ha-to-FUV ratios and thus appear to be more dominated by the current generation of stars than are other parts of the galaxy. However, young sources do exist elsewhere and are particularly conspicuous along the bar. The small-aperture analysis shows three candidate regions for sequential star formation. Surface brightness proÐles are consistent with an exponential disk in both the FUV and the optical continuum.
From Globular Clusters to Tidal Dwarfs: Structure Formation in the Tidal Tails of Merging Galaxies
The Astronomical Journal, 2003
Using V and I images obtained with the Wide Field Planetary Camera 2 (WFPC2) of the Hubble Space Telescope, we investigate compact stellar structures within tidal tails. Six regions of tidal debris in the four classic "Toomre Sequence" mergers: NGC 4038/39 ("Antennae"), NGC 3256, NGC 3921, and NGC 7252 ("Atoms for Peace") have been studied in order to explore how the star formation depends upon the local and global physical conditions. These mergers sample a range of stages in the evolutionary sequence and tails with and without embedded tidal dwarf galaxies. The six tails are found to contain a variety of stellar structures, with sizes ranging from those of globular clusters up to those of dwarf galaxies. From V and I WFPC2 images, we measure the luminosities and colors of the star clusters. NGC 3256 is found to have a large population of blue clusters (0.2 V − I 0.9), particularly in its Western tail, similar to those found in the inner region of the merger. In contrast, NGC 4038/39 has no clusters in the observed region of the tail, only less luminous point sources likely to be individual stars. NGC 3921 and NGC 7252 have small populations of clusters along their tails. A significant cluster population 2
NGC 2782: a merger remnant with young stars in its gaseous tidal tail★
Monthly Notices of the Royal Astronomical Society, 2012
We have searched for young star-forming regions around the merger remnant NGC 2782. By using Galaxy Evolution Explorer far-ultraviolet and near-ultraviolet imaging and H I data we found seven ultraviolet sources, located at distances greater than 26 kpc from the centre of NGC 2782, and coinciding with its western H I tidal tail. These regions were resolved in several smaller systems when Gemini/Gemini multi-object spectrograph (GMOS) r-band images were used. We compared the observed colours to stellar population synthesis models and found that these objects have ages of ∼1 to 11 Myr and masses ranging from 10 3.9 to 10 4.6 M. By using Gemini/GMOS spectroscopic data we confirm memberships and derive high metallicities for three of the young regions in the tail (12+log(O/H) = 8.74 ± 0.20, 8.81 ± 0.20 and 8.78 ± 0.20). These metallicities are similar to the value presented by the nuclear region of NGC 2782 and also similar to the value presented for an object located close to the main body of NGC 2782. The high metallicities measured for the star-forming regions in the gaseous tidal tail of NGC 2782 could be explained if they were formed out of highly enriched gas which was once expelled from the centre of the merging galaxies when the system collided. An additional possibility is that the tail has been a nursery of a few generations of young stellar systems which ultimately polluted this medium with metals, further enriching the already pre-enriched gas ejected to the tail when the galaxies collided.
Ultraviolet Signatures of Tidal Interaction in the Giant Spiral Galaxy M101
The Astrophysical Journal, 1997
We present new evidence for tidal interactions having occurred in the disk of M101 in the last 10 8 -10 9 years. Recent imaging of the far-ultraviolet emission from M101 by the Shuttle-borne Ultraviolet Imaging Telescope (UIT) reveals with unprecedented clarity a disk-wide pattern of multiple linear arm segments ("crooked arms"). The deep FUV image also shows a faint outer spiral arm with a ("curly tail") feature that appears to loop around the supergiant HII region NGC 5471 -linking this outlying starburst with the rest of the galaxy. These FUV-bright features most likely trace hot O & B-type stars along with scattered light from associated nebular dust. Counterparts of the outermost "crooked arms" are evident in maps at visible wavelengths and in the 21-cm line of HI. The inner-disk FUV arms are most closely associated with Hα knots and the outer (downstream) sides of CO arms. Comparisons of the "crooked arm" and "curly tail" morphologies with dynamical simulations yield the greatest similitude, when the nonaxisymmetric forcing comes from a combination of external interactions with one or more companion galaxies and internal perturbations from massive objects orbiting within the disk. We speculate that NGC 5471 represents one of these "massive disturbers" within the disk, whose formation followed from a tidal interaction between M101 and a smaller galaxy.
Observations of a Tidal Tail in the Interacting Galaxies NGC 4485/4490
The Astronomical Journal, 1998
NGC 4485 and NGC 4490 are closely interacting spiral galaxies in the NGC 4631 Group, separated by a projected distance of 7.7 kpc. Images in the B and I bands were obtained with the Burrell Schmidt telescope at Kitt Peak National Observatory in order to study star-forming regions in their tidal features, including a previously undetected faint tail whose color matches that of the outer disk in NGC 4490. A comparison of the tidal morphology with published simulations suggests that this is a prograde encounter with perigalacticon about 4 ] 108 yr ago. This time is approximately the age of the youngest regions in the tail, based on a comparison of observed B[I colors with evolutionary models. Calculations of the Q instability parameter using a rotation curve derived from published H I observations support the conclusion that the tail is currently stable against star formation.
Far‐Ultraviolet Imagery of the Edge‐on Spiral Galaxy NGC 4631
The Astrophysical Journal, 2001
Far ultraviolet (F U V ) imagery of the edge-on, Sc/SBd galaxy, NGC 4631 reveals very strong F U V emission, resulting from active star formation, uniformly distributed along the galactic midplane. Multi-band imagery, H I and H II position-velocity curves and extinction considerations all imply that the emission is from the outer edges of the visible galaxy. The overall F U V morphology of this edge-on disk system is remarkably similar to those of the so-called "chain galaxies" evident at high redshift, thus suggesting a similar interpretation for at least some of those distant objects. F U V, U, B and V magnitudes, measured for 48 star forming regions, along with corresponding Hα and Hβ measurements are used to construct diagnostic color-color diagrams. Although there are significant exceptions, most of the star forming regions are less massive and older than 30 Doradus. Comparison with the expectations from two star formation models yields ages of 2.7 to 10 Myr for the instantaneous burst (IB) model and star formation cut-off ages of 0 to 9 Myr for the continuous star formation (CSF) model. Interpreted in terms of the IB model the photometry implies a total created mass in the 48 star forming regions of 2.5×10 7 M ⊙ . When viewed as resulting from constant star formation the photometry implies a star formation rate of 0.33 M ⊙ yr −1 . These results are compared to those derived from FIR and radio observations. Corrections for F U V emission reprocessed by interstellar grains are estimated.
Giant Molecular Clouds and Star Formation in the Tidal Molecular Arm of NGC 4039
The Astrophysical Journal, 2012
The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which in principle are different from quasi stationary spiral arms. We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies, with a resolution of 1. 68 × 0. 85, using the Atacama Large Millimeter/submillimeter Array science verification CO(2-1) data. The arm extends 3.4 kpc (34 ) and is characterized by widths of 200 pc (2 ) and velocity widths of typically ∆V 10-20 km s −1 . About 10 clumps are strung out along this structure, most of them unresolved, with average surface densities of Σ gas 10-100 M pc −2 , and masses of (1-8)×10 6 M . These structures resemble the morphology of beads on a string, with an almost equidistant separation between the beads of about 350 pc, which may represent a characteristic separation scale for giant molecular associations. We find that the star formation efficiency at a resolution of 6 (600 pc) is in general a factor of 10 higher than in disk galaxies and other tidal arms and bridges. This arm is linked, based on the distribution and kinematics, to the base of the western spiral arm of NGC 4039, but its morphology is different to that predicted by high-resolution simulations of the Antennae galaxies.
The Astrophysical Journal, 2007
We present the results from the analysis of optical spectra of 31 Hα-selected regions in the extended UV (XUV) disks of M 83 (NGC 5236) and NGC 4625 recently discovered by GALEX. The spectra were obtained using IMACS at Las Campanas Observatory 6.5m Magellan I telescope and COSMIC at the Palomar 200-inch telescope, respectively for M 83 and NGC 4625. The line ratios measured indicate nebular oxygen abundances (derived from the R23 parameter) of the order of Z ⊙ /5-Z ⊙ /10 1 . For most emission-line regions analyzed the line fluxes and ratios measured are best reproduced by models of photoionization by single stars with masses in the range 20-40 M ⊙ and oxygen abundances comparable to those derived from the R23 parameter. We find indications for a relatively high N/O abundance ratio in the XUV disk of M 83. Although the metallicities derived imply that these are not the first stars formed in the XUV disks, such a level of enrichment could be reached in young spiral disks only 1 Gyr after these first stars would have formed. The amount of gas in the XUV disks allow maintaining the current level of star formation for at least a few Gyr.