Clumpy Galaxies Research Articles

ACCRETION-DRIVEN TURBULENCE AND THE TRANSITION TO GLOBAL INSTABILITY IN YOUNG GALAXY DISKS

A simple model of gas accretion in young galaxy disks suggests that fast turbulent motions can be driven by accretion energy for a time t_acc~2(epsilon^{0.5} GM^2/xi V^3)^{0.5} where epsilon is the fraction of the accretion energy going into disk turbulence, M and V are the galaxy mass and rotation speed, and xi is the accretion rate. After t_acc, accretion is replaced by disk instabilities as a source of turbulence driving, and shortly after that, energetic feedback by young stars should become important. The star formation rate equilibrates at the accretion rate after 1 to 2 t_acc, depending on the star formation efficiency per dynamical time. The fast turbulence that is observed in high redshift starburst disks is not likely to be driven by accretion because the initial t_acc phase is over by the time the starburst is present. However, the high turbulent speeds that must have been present earlier, when the observed massive clumps first formed, could have been driven by accretion energy. The combined observations of a high relative velocity dispersion in the gas of z~2 clumpy galaxies and a gas mass comparable to the stellar mass suggests that either the star formation efficiency is fairly high, perhaps 10x higher than in local galaxies, or the observed turbulence is powered by young stars.

CLUMPY GALAXIES IN GOODS AND GEMS: MASSIVE ANALOGS OF LOCAL DWARF IRREGULARS

Clumpy galaxies in the Galaxy Evolution from Morphology and SEDs and Great Observatories Origins Deep Survey fields are examined for clues to their evolution into modern spirals. The magnitudes of the clumps and the surface brightnesses of the interclump regions are measured and fitted to models of stellar age and mass. There is an evolutionary trend from clump clusters with no evident interclump emission to clump clusters with faint red disks, to spiral galaxies of the flocculent or grand design types. Along this sequence, the interclump surface density increases and the mass surface density contrast between the clumps and the interclump regions decreases, suggesting a gradual dispersal of clumps to form disks. Also along this sequence, the bulge-to-clump mass ratios and age ratios increase, suggesting a gradual formation of bulges. All of these morphological types occur in the same redshift range, indicating that the clump cluster morphology is not the result of bandshifting. This redshift range also includes clear examples of interacting galaxies with tidal tails and other characteristic features, indicating that clump clusters, which do not have these features, are not generally interacting. Comparisons to local galaxies with the same rest wavelength and spatial resolution show that clump clusters are unlike local flocculent and spiral galaxies primarily because of the high clump/interclump contrasts in the clump clusters. They bear a striking resemblance to local dwarf irregulars, however. This resemblance is consistent with a model in which the clumpy morphology comes from gravitational instabilities in gas with a high turbulent speed compared to the rotation speed and a high mass fraction compared to the stars. The morphology does not depend on galaxy mass as much as it depends on evolutionary stage: clump clusters are 100 times more massive than local dwarfs. The apparent lack of star formation in damped Lyman alpha absorbers may result from fast turbulence.

Disc formation and the origin of clumpy galaxies at high redshift

Abstract Observations of high-redshift galaxies have revealed a multitude of large clumpy rapidly star-forming galaxies. Their formation scenario and their link to present-day spirals are still unknown. In this Letter, we perform adaptive mesh refinement simulations of disc formation in a cosmological context that are unrivalled in terms of mass and spatial resolution. We find that the so-called ‘chain-galaxies’ and ‘clump-clusters’ are a natural outcome of early epochs of enhanced gas accretion from cold dense streams as well as tidally and ram-pressured stripped material from minor mergers and satellites. Through interaction with the hot halo gas, this freshly accreted cold gas settles into a large disc-like system, not necessarily aligned to an older stellar component, that undergoes fragmentation and subsequent star formation, forming large clumps in the mass range 107–109 M⊙. Galaxy formation is a complex process at this important epoch when most of the central baryons are being acquired through a range of different mechanisms – we highlight that a rapid mass loading epoch is required to fuel the fragmentation taking place in the massive arms in the outskirts of extended discs, an accretion mode that occurs naturally in the hierarchical assembly process at early epochs.

STRUCTURES OF LOCAL GALAXIES COMPARED TO HIGH-REDSHIFT STAR-FORMING GALAXIES

The rest-frame far-ultraviolet (FUV) morphologies of 8 nearby interacting and starburst galaxies (Arp 269, M 82, Mrk 8, NGC 520, NGC 1068, NGC 3079, NGC 3310, NGC 7673) are compared with 54 galaxies at z ~ 1.5 and 46 galaxies at z ~ 4 observed in the GOODS-ACS field. The nearby sample is artificially redshifted to z ~ 1.5 and 4. We compare the simulated galaxy morphologies to real z ~ 1.5 and 4 UV-bright galaxy morphologies. We calculate the Gini coefficient (G), the second-order moment of the brightest 20% of the galaxy's flux (M_20), and the Sersic index (n). We explore the use of nonparametric methods with 2D profile fitting and find the combination of M_20 with n an efficient method to classify galaxies as having merger, exponential disk, or bulge-like morphologies. When classified according to G and M_20, 20/30% of real/simulated galaxies at z ~ 1.5 and 37/12% at z ~ 4 have bulge-like morphologies. The rest have merger-like or intermediate distributions. Alternatively, when classified according to the Sersic index, 70% of the z ~ 1.5 and z ~ 4 real galaxies are exponential disks or bulge-like with n > 0.8, and ~30% of the real galaxies are classified as mergers. The artificially redshifted galaxies have n values with ~35% bulge or exponential at z ~ 1.5 and 4. Therefore, ~20-30% of Lyman-break galaxies (LBGs) have structures similar to local starburst mergers, and may be driven by similar processes. We assume merger-like or clumpy star-forming galaxies in the GOODS field have morphological structure with values n -1.7. We conclude that Mrk 8, NGC 3079, and NGC 7673 have structures similar to those of merger-like and clumpy star-forming galaxies observed at z ~ 1.5 and 4.

REST-FRAME UV VERSUS OPTICAL MORPHOLOGIES OF GALAXIES USING SÉRSIC PROFILE FITTING: THE IMPORTANCE OF MORPHOLOGICALK-CORRECTION

We show a comparison of the rest-frame UV morphologies of a sample of 162 intermediate redshift (median redshift 1.02) galaxies with their rest-frame optical morphologies. We select our sample from the deepest near-UV image obtained with the Hubble Space Telescope (HST) using the WFPC2 (F300W) as part of the parallel observations of the Hubble Ultra Deep Field campaign overlapping with the HST/ACS GOODS dataset. We perform single component Sersic fits in both WFPC2/F300W (rest-frame UV) and ACS/F850LP (rest-frame optical) bands and deduce that the Sersic index $n$ is estimated to be smaller in the rest-frame UV compared to the rest-frame optical, leading to an overestimation of the number of merger candidates by ~40-100% compared to the rest-frame optical depending upon the cutoff in $n$ employed for identifying merger candidates. This effect seems to be dominated by galaxies with low values of n(F300W) <= 0.5 that have a value of n(F850LP) ~ 1.0. We argue that these objects are probably clumpy starforming galaxies or minor mergers, both of which are essentially contaminants, if one is interested in identifying major mergers. In addition we also find evidence that the axis ratio b/a is lower, i.e. ellipticity (1-b/a) is higher in rest-frame UV compared to the rest-frame optical. Moreover, we find that in the rest-frame UV, the number of high ellipticity (e >= 0.8) objects are higher by a factor of ~2.8 compared to the rest-frame optical. This indicates that the reported dominance of elongated morphologies among high-z LBGs might just be a bias related to the use of rest-frame UV datasets in high-z studies.

Nuclear Black Hole Formation in Clumpy Galaxies at High Redshift

Massive stellar clumps in high-redshift galaxies interact and migrate to the center to form a bulge and exponential disk in 1 Gyr. Here we consider the fate of intermediate-mass black holes (BHs) that might form by massive-star coalescence in the dense young clusters of these disk clumps. We find that the BHs move inward with the clumps and reach the inner few hundred parsecs in only a few orbit times. There they could merge into a supermassive BH by dynamical friction. The ratio of BH mass to stellar mass in the disk clumps is approximately preserved in the final ratio of BH to bulge mass. Because this ratio for individual clusters has been estimated to be ~10−3, the observed BH-to-bulge mass ratio results. We also obtain a relation between BH mass and bulge velocity dispersion that is compatible with observations of present-day galaxies.

Observations and modeling of a clumpy galaxy atz = 1.6

We investigate the properties of a clump-cluster galaxy at redshift 1.57. In optical observations, the morphology of this galaxy is dominated by eight star-forming clumps, and its photometric properties are typical of most clump-cluster and chain galaxies. Its complex asymmetrical morphology has led to the suggestion that this system is a group merger of several initially separate proto-galaxies. We performed Hα integral field spectroscopy of this system using SINFONI on VLT UT4. These observations reveal a large-scale velocity gradient throughout the system, but with large local kinematic disturbances. Using a numerical model of gas-rich disk fragmentation, we find that clump interactions and migration can explain the observed disturbed rotation. On the other hand, the global rotation would not be expected for a multiply merging system. We also find that this system follows the relations of stellar mass versus metallicity, star formation rate, and size that are expected for a disk at this redshift. Furthermore, the galaxy exhibits a disk-like radial metallicity gradient. A formation scenario of internal disk fragmentation is therefore the most likely one. A red and metallic central concentration appears to be a bulge in this proto-spiral clumpy galaxy. A chain galaxy at redshift 2.07 in the same field also shows disk-like rotation. Such systems are likely progenitors of present-day bright spiral galaxies, which shape their exponential disks through clump migration and disruption, a process that in turn fuels their bulges. Our results show that disturbed morphologies and kinematics are not necessarily signs of galaxy mergers and interactions, but may instead be produced by the internal evolution of primordial disks.

Probing clumpy pasts of galaxies from asymptotic giant branch stars

Abstract Recent morphological studies of galaxies by the Hubble Space Telescope (HST) have revealed that actively star-forming galaxies at intermediate and high redshifts (z= 0.5–2.0) have very clumpy and irregular distributions of stars. It is however unclear whether and how these clumpy galaxies evolve into the present spiral and elliptical galaxies with regular shapes. We here propose that spatial distributions of asymptotic giant branch (AGB) stars, probing the different mean age and metallicity of the underlying stellar population, can provide vital clues to the evolution of these clumpy galaxies, in particular, those at intermediate redshifts. In order to demonstrate this proposal to be quite promising, we show the results of test-particle simulations on the long-term dynamical evolution of unbound groups of AGB stars (‘stellar clumps’), which correspond to the successors of star-forming clumps at intermediate redshifts, in isolated and interacting galaxies. We particularly show that azimuthal distributions of AGB stars dispersed from stellar clumps as a result of gravitational interaction with their host galaxies can still be inhomogeneous several Gyr after stellar clump formation for some models. We also show that the inhomogeneities in the azimuthal distributions of dispersed AGB stars can disappear more quickly in stellar clumps with larger sizes and higher velocity dispersions. These results suggest that if apparently clumpy structures of galaxies at intermediate redshifts are due to stars in unbound or weakly bound clusters, spatial distributions of AGB stars can have fossil records on past clumpy structures of galaxies. As an example, we compare the latest observations on the spatial distributions of AGB stars in the Large and Small Magellanic Clouds (LMC and SMC, respectively) with the corresponding simulations, and thereby discuss whether the LMC and the SMC had massive star-forming clumps in their outer discs a few to several Gyr ago.

Resolved Galaxies in the Hubble Ultra Deep Field: Star Formation in Disks at High Redshift

The photometric redshift distributions, spectral types, Sersic indices, and sizes of all resolved galaxies in the Hubble Space Telescope Ultra Deep Field (UDF) are studied in order to understand the environment and nature of star formation in the early Universe. Clumpy disk galaxies that are bright at short wavelengths (restframe <5000 Angstroms) dominate the UDF out to z~5.5. Their uniformity in V/V_max and co-moving volume density suggest they go even further, spanning a total time more than an order of magnitude larger than their instantaneous star formation times. They precede as well as accompany the formation epoch of distant red galaxies and extreme red objects. Those preceding could be the pre-merger objects that combined to make red spheroidal types at z~2 to 3. Clumpy disks that do not undergo mergers are likely to evolve into spirals. The morphology of clumpy disks, the size and separation of the clumps, and the prevalence of this type of structure in the early Universe suggests that most star formation occurs by self-gravitational collapse of disk gas.

Clumpy Galaxies in the Early Universe

AbstractClumpy galaxies are prominent in the early Universe. We present morphological and photometric properties of a wide range of galaxy types and their star-forming clumps in the Hubble Ultra Deep Field. Sizes, scale lengths, and scale heights suggest that galaxies grow by a factor of 2 fromz= 4 to the present, and that thick disks are present in the early Universe. The largest clumps of star formation are 107–109M⊙in different galaxies, much more massive than large star-forming complexes in local galaxies. Dissolved clumps may account for both the exponential disks and the early thick disks of spirals and proto-spiral galaxies.

Clumpy outer Galaxy molecular clouds and the steepening of the IMF

We report the results of high-resolution (~0.2 pc) CO(1-0) and CS(2-1) observations of the central regions of three star-forming molecular clouds in the far-outer Galaxy (~16 kpc from the Galactic Center): WB89 85 (Sh 2-127), WB89 380, and WB89 437. We used the BIMA array in combination with IRAM 30-m and NRAO 12-m observations. The GMC's in which the regions are embedded were studied by means of KOSMA 3-m CO(2-1) observations. The properties the CO and CS clumps are analyzed and compared with newly derived results of previously published single-dish measurements of local clouds (OrionB South and Rosette). We find that the slopes of the clump mass distributions (-1.28 and -1.49, for WB89 85 and WB89 380, respectively) are somewhat less steep than found for most local clouds, but similar to those of clouds which have been analyzed with the same clumpfind program. We investigate the clump stability by using the virial theorem, including all possible contributions (gravity, turbulence, magnetic fields, and pressure due to the interclump gas). It appears that under reasonable assumptions a combination of these forces would render most clumps stable. Comparing only gravity and turbulence, we find that in the far-outer Galaxy clouds, these forces are in equilibium (virial parameter alpha~1) for clumps down to the lowest masses found (a few Msol). For clumps in the local clouds alpha~1 only for clumps with masses larger than a few tens of Msol. Thus it appears that in these outer Galaxy clumps gravity is the dominant force down to a much lower mass than in local clouds, implying that gravitational collapse and star formation may occur more readily even in the smallest clumps. Although there are some caveats, due to the inhomogeneity of the data used, this might explain the apparently steeper IMF found in the outer Galaxy.

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)

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).

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).

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.

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.

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.

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.