Clumpy Irregular Galaxies Research Articles

Starburst galaxy NGC 7673: a minor merger remnant

We investigate the kinematics of the luminous starburst galaxy NGC 7673 = Mrk 325, a nearby example of a ‘clumpy irregular galaxy’. Images with the WIYN 3.5m telescope reveal outer wisps associated with mergers, and we suggest NGC 7673 is the survivor of a minor merger. DensePak spectroscopy of the Hα kinematics shows that the H II regions are confined to a rotating disk. The Hα emission line velocity field indicates that although there is widespread star formation across the inner disk, it is still rotating smoothly. The Hα emission profiles over the brightest regions of the galaxy have two components: narrow, FWHM ≈ 50kms−1 lines, and broad, FWHMW ≈ 150 km s−1 lines. The width of the narrow lines is likely due to a combination of averaging effects, stellar winds and SNRs, and possibly gravitational motions within the disk. The origin of the broad component, which eclipses the narrow component in flux over much of the galaxy's inner regions, is still unclear. We may be looking at turbulent gas encased in bubbles carved out by massive stars and their descendants, or possibly some localized outflows from the disk.

The clumpy galaxy Markarian 297 and its supernova activity

view Abstract Citations (21) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Clumpy Galaxy Markarian 297 and Its Supernova Activity Yin, Q. F. Abstract I present radio observations of the clumpy irregular galaxy Mrk 297 (= NGC 6052) made with the VLA at 20, 6, 3.6, and 2 cm from 1980 January to 1992 April, which show that the variable, compact source (Mrk 297A) is a single supernova with the highest peak radio luminosity known for a supernova. Twenty-one VLA flux-density measurements at four wavelengths of the compact source, obtained over the past 12 yr, yield a satisfactory fit to Chevalier's model for supernova light curves. Shorter period fluctuations in the observations are significant and are consistent with refractive interstellar scintillation. The supernova rate for the entire galaxy can be estimated from a global formula (Condon & Yin 1990) which uniquely relates total nonthermal radio emission to supernova rate. The resulting supernova rate estimated for the entire galaxy Mrk 297 is high (0.3 yr^-1^).However, most individual Type II radio supernovae are too weak to be detected at the distance of Mrk 297. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173548 Bibcode: 1994ApJ...420..152Y Keywords: Galactic Clusters; Irregular Galaxies; Light Curve; Markarian Galaxies; Star Formation Rate; Supernovae; Emission Spectra; Luminosity; Radio Astronomy; Radio Emission; Very Large Array (Vla); X Ray Spectra; Astrophysics; GALAXIES: STELLAR CONTENT; GALAXIES: INDIVIDUAL NAME: MARKARIAN 297; RADIO CONTINUUM: GALAXIES; STARS: SUPERNOVAE: GENERAL full text sources ADS | data products SIMBAD (7) NED (6)

Spectroscopic and photometric investigation of the clumpy irregular galaxy Markarian 1006

Spectroscopic and photometric investigation of the clumpy irregular galaxy Markarian 1006

Two radio supernovae in the unusual galaxy Markarian 297

STARBURST galaxies have higher star formation and supernova rates than normal galaxies, triggered in many cases by the interaction of two galaxies1. Direct estimates of the supernova rate in starburst galaxies is difficult, because optical direction of super-novae is hampered by high background brightness and by dust2, both of which are associated with the starburst phenomenon. Radio observations do not suffer from these problems. We report here the discovery of two radio supernovae in the clumpy irregular galaxy Markarian 297 (Mkn 297, also known as NGC6052), which has been estimated3 to have a star formation rate ten times that of a normal spiral galaxy, and a supernova rate of 0.3–0.5 per year. It may consist of two interacting galaxies4. A variable radio source found in 1982 (ref. 5) was attributed to possible supernova activity, and our observations with the Very Large Array, combined with earlier published data, define a reasonable radio light curve for a supernova that exploded in July 1979. The variability resembles that of the young supernova SN1986J (ref. 6), but at maximum the supernova in Mkn 297 would have been about six times as bright. We also identify a second source in the galaxy as a supernova. The presence of two extraordinarily bright supernovae in the same region may be a particular result of the interaction between two galaxies.

Wing galaxies - A formation mechanism of the clumpy irregular galaxy Markarian 297

In order to contribute to an understanding of collision-induced starburst activities, the authors present a detailed case study on the starburst galaxy Markarian 297 (= NGC 6052 = Arp 209; hereafter Mrk 297). This galaxy is classified as a clumpy irregular galaxy (CIG) according to its morphological properties (cf. Heidmann, 1987). Two major clumps and many small clumps are observed in the entire region of Mrk 297 (Hecquet, Coupinot, and Maucherat 1987). The overall morphology of Mrk 297 is highly chaotic and thus it seems difficult to determine possible orbits of galaxy-galaxy collision. However, the authors have serendipitously found a possible orbit during a course of numerical simulations for a radial-penetration collision between galaxies. The radial-penetration collision means that an intruder penetrates a target galaxy radially passing by its nucleus. This kind of collision is known to explain a formation mechanism of ripples around disk galaxies (Wallin and Struck-Marcell 1988). Here, the authors show that the radial-penetration collision between galaxies successfully explains both overall morphological and kinematical properties of Mrk 297. The authors made two kinds of numerical simulations for Mrk 297. One is N-body (1x10(exp 4) particles) simulations in which effects of self gravity of the stellar disk are taken into account. These simulations are used to study detailed morphological feature of Mrk 297. The response of gas clouds are also investigated in order to estimate star formation rates in such collisions. The other is test-particle simulations, which are utilized to obtain a rough picture of Mrk 297 and to analyze the velocity field of Mrk 297. The techniques of the numerical simulations are the same as those in Noguchi (1988) and Noguchi and Ishibashi (1986). In the present model, an intruding galaxy with the same mass of a target galaxy moves on a rectilinear orbit which passes the center of the target.

Wing Galaxies: A Formation Mechanism of the Clumpy Irregular Galaxy Marrarian 297

In order to contribute to an understanding of collision-induced staxburst activities, we present a detailed case study on the staxburst galaxy Maxkaxian 297 (= NGC 6052 = Arp 209; hereafter Mrk 297). This galaxy is classified as a clumpy irregular galaxy (hereafter CIGs) according to its morphological properties (cf. Heidmann, 1987). Two major clumps and many small clumps are observed in the entire region of Mrk 297 (Hecquet, Coupinot, and Maucherat 1987). A typical major clump of CIGs has a diameter of a few hundred pc and its dynamical mass is estimated as an order of 108M⊙ (Taniguchi and Tamura 1987).

Far-Infrared Emission from Clumpy Irregular Galaxies

The four clumpy irregular galaxies Mkr 8, 296,297 and 325 have been observed by IRAS. All galaxies have been detected in at least two of the four detector bands. The ratios of the 100 to 60-m flux densities are comparable to those of HII regions or violently star forming galaxies. The average star formation rate in clumpy irregular galaxies is of the order of a few solar masses per year (based on their average far-infrared luminosity and a Hubble constant of 75 km s−1 Mpc−1.

Hyperactive Star Bursts in Clumpy Irregular Galaxies

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.

High-Dispersion Spectroscopy of the Clumpy Irregular Galaxies Markarian 297 and 325

High-dispersion spectroscopic observations with good spectral resolution have been made of the four clumps in the two clumpy irregular galaxies Markarian 297 and 325. Their velocity dispersions in the Hα emission line (32-41 km s−1) are larger by about 2 or more than those of the so-called giant HII regions in nearby spiral or irregular galaxies.

U-G and G-R Colors of the Clumpy Irregular Galaxies Markarian 297 and 325

U-G and G-R colors of clumps in Mrk 297 and Mrk 325 are presented. In addition, colors of other interesting objects and radiation sources were calculated for the Kiso UGR system. These objects are used to interpret the intrinsic characteristics of our sample. The observed colors of the clumps in both Mrk 297 and Mrk 325 are bluer than Im galaxies as well as main sequence stars and show scatter over the extent of the U-G vs. G-R diagram.

Photometric, Spectroscopic and 21-cm Line Investigation of Selected UV-Excess KISO and Clumpy Galaxies

A survey of Kiso UV-excess galaxies (KUGs) has been made using the 105-cm Kiso Schmidt telescope. We selected three galaxies of Ic-type (i.e. irregulars with clumpy HII regions). KUGs 1618+373, 1624+404 and 1626+413, and observed them together with a clumpy irregular galaxy Mrk 297 to clarify their star formation activity (Maehara et al. 1986).

The X-Ray Emission of a Clumpy Irregular Galaxy from Thousands of Supernova Remnants?

Clumpy irregular galaxies contain 5–10 “clumps” which are hyperactive HII complexes each equivalent to 100 giant HII regions of the 30 Doradus type (Heidmann 1982). We observed one of them, Mkn 325 (= NGC 7673), with the Einstein IPC in Dec. 1980 (seq.no 10201) for 3,200 s. The reduction was made kindly by D.E. Harris. The source was localized at 23h 25m 12.2s, + 23° 18′ 25″ (1950) in agreement with the optical position, at a quite weak level (14 counts in the 1.4–2.9 kev range). Thus we could not get valuable spectral information, only that the spectrum is rather not soft. Correction for galactic absorption NH = 5 ×1020 at.cm−2 (Heyles 1975) is applied. Fits of power law spectra happen to all go through the point with flux density 4.5 ×10−5 mJy at 3.0 ×1017 Hz (1.24 kev) and they yield a flux (1.1 ± 0.3) x10−13 erg cm−2 s−1 inside 1–3 kev and an X-luminosity (2.2 ± 0.3)×1041 erg s−1 inside 0.5–4.5 kev, for a distance 49 Mpc.

Radio Observations of Markarian 8

Markarian 8, a clumpy irregular galaxy (Casini et al. 1979), was observed with the VLA at 20 cm (Mar. 19, 1981; 26 ant.) and 6 cm wavelengths (June 12, 1980; 18 ant.) The structure is alike at the two wavelengths, consisting of 3 distinct clumps imbedded in a diffuse envelope of about 40 arcsec extent. Figure 1 shows the 6 cm structure. At higher resolution the clumps break up into several components. The 20 cm structure is shown in Figure 2, which also compares the optical and radio morphologies. There is excellent general agreement, suggesting a common origin of emission in the clumps.

Star formation and chemical abundances in clumpy irregular galaxies

Clumpy irregular galaxies consist of several bright clumps which are huge H II complexes (about 100 times brighter and more massive than 30 Doradus) and contain about 10/sup 5/ O and B stars. Image-tube spectrograms with 1--3 A resolution have been obtained of the brightest emission regions of three clumpy galaxies and one candidate clumpy galaxy with the Mauna Kea 2.24 m telescope. The electron temperatures were found to be in the range 7000--9000 K and electron densities a few hundred cm/sup 3/: quite typical for normal H II regions. The abundances of O, N. S in Mrk 432 are comparable to those in Orion, while the three clumpy galaxies are slightly deficient in O and S (by factors of 2 to 4) and N (by factors of 3 to 6). The galaxies appear to be normal (like Sc galaxies) in mass and composition. Supernovae remnants are indicated by the high (S II)/H..cap alpha.. ratio. Possible triggering mechanisms for the exceptional star formation activity are discussed.

IUE UV spectra of the clumpy irregular galaxy MKN297

Clumpy irregular galaxies are made up of 5–10 bright clumps loosely scattered in a common envelope, have excess near-UV radiation and are giant compared with classic irregular galaxies1,2. Clumps are apparently ∼100 times more massive than giant H II regions such as 30 Doradus or NGC604 (ref. 3). To get an insight into their properties we have obtained UV spectra using the IUE satellite of one of the clumpy irregular galaxies, MKN297. The UV continuum spectrum thus obtained follows a power law and is steeper (fainter at short wavelengths) than that of a classic irregular or late galaxy. The 155 nm intrinsic luminosity is 400 times larger than that of 30 Doradus. The observed absorption lines can be attributed to early O or B stars, and no emission lines are detectable. We report here that the spectra indicate that each of the clumps contain ∼104 early stars and are supergiant H II regions in which exceptional bursts of star formation take place.