High resolution imagery of the clumpy irregular galaxy Markarian 325 = NGC 7673

Coupinot, G.; Hecquet, J.; Heidmann, J.

doi:10.1093/mnras/199.2.451

Cited by 14 publications

(11 citation statements)

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“…The spiral pattern that is prominent in our images also was noted in earlier studies (de Vaucouleurs et al 1976;Huchra 1977;Coupinot et al 1982). Optical spectra revealed the presence of a broad emission component underlying the narrow lines more commonly associated with H  regions, and a remarkably constant radial velocity across the galaxy (Duflot-Augarde & Alloin 1982;Taniguchi & Tamura 1987;Homeier & Gallagher 1999).…”

Section: Properties Of Ngc 7673supporting

confidence: 86%

The star cluster system of the NGC 7673 starburst

Homeier

Gallagher

Pasquali³

2002

A&A

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Abstract. We investigate the star cluster system in the starburst galaxy NGC 7673 using archival Hubble Space Telescope WFPC2 broad-band images. For the first time we are able to examine the internal structures of the prominent optical clumps in this galaxy. The clumps are composed of young stars, 16-33% of which are in bright star clusters. We identify 268 star cluster candidates in both the F555W and F814W images, and 50 clusters with the F255W filter. These data allow us to estimate ages and masses using color-magnitude and two-color diagrams for our sample. We find a population of young, <6 Myr clusters located throughout the galaxy with concentrations in the clumps. Star cluster mass estimates are 5-50 × 10 4 M for the brightest objects. The starburst remains active in physically well-separated regions, indicating a widespread starburst trigger. We discuss clump lifetimes, their implications for the future evolution of NGC 7673, and possible relationships to high redshift starbursts.

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Section: Properties Of Ngc 7673supporting

confidence: 86%

The star cluster system of the NGC 7673 starburst

Homeier

Gallagher

Pasquali³

2002

A&A

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“…Bursts have been suggested for various high surface brightness Irrs fr om a comparison of evolutionary models of stellar populations with observed broadband colors fo r late-type galaxies (15,220,313,333,349), from colors and emission-line strengths in Markarian galaxies (177,178), from popUlation studies fo r the Magellanic Clouds (8,43,122,168) and M82 (257), from metallicity enrichment rate arguments (4,225,226,258,361), from radio observations of Markarian galaxies (33, 148a), and from star cluster studies ofNGC 5253 (370), to name a few examples. Similarly, amorphous galaxies such as NGC 1705, which appear to be involved in OB star fo rmation at high rates over most of their optical dimensions, are likely to be in burst phases (22,219), as are clumpy Irrs (66). It is also evident from the prevalence of very blue galaxies in binary systems that interactions affect star fo rmation processes and may stimulate bursts (10,11,31,201,220).…”

Section: Bursts Of Star Fo Rmationmentioning

confidence: 99%

“…giant blue compacts and clumpy irregulars. These systems have moderate-to-solar metallicities (36, 120, 342 ; Gallagher, Hunter & Bushouse, in preparation) and rotate at velocities similar to spirals, but they produce OB stars on incredible scales and in chaotic fashions that lead to Irr morphologies (66,273,274). The processes that cause such extreme (and probably transitory) evolutionary events in spirallike galaxies are not known, but they could include interactions with other galaxies or external agents (e.g.…”

Section: Ssp Sf: a Possible Modelmentioning

confidence: 99%

Structure and Evolution of Irregular Galaxies

Gallagher¹,

Hunter²

1984

Annu. Rev. Astron. Astrophys.

116

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INTRODUCTIONIrregular galaxies (Irrs) usually are smaller, less massive, and optically dimmer than commonly studied giant spirals, SOs, and classical ellipticals. At first giance they also appear to be rare objects that make up only a few percent of the major bright galaxy catalogs (87, 300). Is there then much reward in pursuing such faint and elusive galaxies? The answer to this question turns out to be a surprisingly strong "yes." An examination of more nearly complete samples of galaxies (213,341,366) reveals that Irrs account for it substantial (1/3-1/2) fraction of all galaxies, and that they certainly are dominant by number density among actively star-forming galaxies. A diversity of nearby examples therefore abound [including, of course, the Large and Small Magellanic Clouds (LMC and SMC)], making Irrs prime targets for detailed investigations of galactic stellar content and star fo rmation processes. Recognition of their structural simplicity has provided an additional stimulus for recent interest in Irrs as tests for theories of galaxy structure and evolution. These galaxies also are comparatively unevolved; and thus they may yield further rewards by allowing conditions to be defined in the poorly understood realm of low density extragalactic systems, which retain considerable information about galaxy formation (101, 327).In the broadest sense, the irregular galaxy class is loosely defined (e.g. see illustrations in 9, 23, 378,379). Hubble (175, 176) originally bu�lt on earlier nebular classification schemes (e.g. 153) and considered galaxies to be "irregular" if they showed chaotic, non symmetrical blue-light distributions, in contrast with the axial symmetry of normal "regular" systems. Later classification systems subdivide irregular galaxies into tWb major groups : Magellanic systems (Irr I, 1m), which resemble the Magellanic Clouds; and peculiar, often amorphous galaxies, which are classified as Irr II or 10 systems (72,174,290,292).Unfortunately, irregular structures may arise from a vari�ty of physical causes, and as a result a wide range of physical types of irregular galaxies are known to exist : (a) There may be substantial chaos in the projected stellar mass distributions in galaxies, although such nonequilibrium structures are unlikely to survive for more than a fe w rotation periods ("" 109 yr). Most currently kilOwn galaxies in disturbed states seem to be involved in galaxy galaxy intetactions (3 11, 358, 359, 384, 392, 393), although newly fo rmed galaxies could also find themselves in this situation (45). Some galaxies classified as Irr II or IO also belong in the category of interacting galaxies. (b) Similarly, unusual distributions of dense interstellar gas across the face of a galaxy may produce an optical image that is mottled by dark lanes. The dusty Irr II galaxies discussed by Krienke & Hodge (214) belong in this group. As these authors note, extended interstellar matter also can lead to emission filaments and reflection nebulae on galactic scales that give rise to abnormal optica...

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“…Most surprisingly, high resolution imagery of this galaxy showed that the clumps have linear sizes not exceeding 500 pc (Fig.6). This means that though clumps have each a 100 times the star forming activity of 30 Doradus proper (the Tarantula Nebula), whose size is 100 pc, their size is not larger than the 500 pc overall dimension o-f the 30 Dor complex, as given for exemple by radio continuum maps (Coupinot et al 1982). This leads to an "olive jar" model in which a clump would be a tight package of 5x5x5, i.e.…”

Section: An "Olive Jar" Modelmentioning

confidence: 99%

Hyperactive Star Bursts in Clumpy Irregular Galaxies

Heidmann

1987

Symp. - Int. Astron. Union

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Clumpy irregular galaxies have been identified as giant irregulars with a clumpy structure. Investigations in the visible, UV, radio centimetric, X-ray and far infrared demonstrated that the clumps are hyperactive bursts of star formation, each equivalent to a hundred giant HII regions like 30 Doradus or NGC 604. In spite of their strong activity, their linear size is smaller than half a kpc, leading to an “olive jar” model with very peculiar physical conditions. These could be related to the non-detection of the 2.6-mm CO line and to our discovery in a clump of the first known case of a strong, compact, variable radio source which is not a galactic nucleus.

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High resolution imagery of the clumpy irregular galaxy Markarian 325 = NGC 7673

Cited by 14 publications

References 0 publications

The star cluster system of the NGC 7673 starburst

The star cluster system of the NGC 7673 starburst

Structure and Evolution of Irregular Galaxies

Hyperactive Star Bursts in Clumpy Irregular Galaxies

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