arXiv subjects

Elias Brinks

Publications and source records attributed to Elias Brinks.

At least 91 records · Page 5Linked to original sources

arXiv2007

Star Formation in NGC 5194 (M51a). II. The Spatially-Resolved Star Formation Law

We have studied the relationship between the star formation rate (SFR) surface density and gas surface density in the spiral galaxy M51a (NGC 5194), using multi-wavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of H-alpha emission-line and 24 micron continuum luminosities, that provides reliable extinction-corrected ionizing fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis HI and CO maps has allowed us to probe the form of the spatially-resolved star formation law on scales of 0.5 to 2 kpc. We find that the resolved SFR vs gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zeropoint and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of areal sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parametrization of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.

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arXiv2007

Tidal Debris posing as Dark Galaxies

Debris sent into the intergalactic medium during tidal collisions can tell us about several fundamental properties of galaxies, in particular their missing mass, both in the form of cosmological Dark Matter and so-called Lost Baryons. High velocity encounters, which are common in clusters of galaxies, are able to produce faint tidal debris that may appear as star-less, free floating HI clouds. These may be mistaken for Dark Galaxies, a putative class of gaseous, dark matter dominated, objects which for some reason never managed to form stars. VirgoHI21 is by far the most spectacular and most discussed Dark Galaxy candidate so far detected in HI surveys. We show here that it is most likely made out of material expelled 750 Myr ago from the nearby spiral galaxy NGC 4254 during its fly--by at about 1000 km/s by a massive intruder. Our numerical model of the collision is able to reproduce the main characteristics of the system: in particular the absence of stars, and its prominent velocity gradient. Originally attributed to the gas being in rotation within a massive dark matter halo, we find it instead to be consistent with a combination of simple streaming motion plus projection effects (Duc & Bournaud, 2007). We discuss several ways to identify a tidal origin in a Dark Galaxy candidate and illustrate the method using another HI system in Virgo, VCC 2062, which is most likely a Tidal Dwarf Galaxy (Duc et al., 2007). Now, whereas tidal debris should not contain any dark matter from the halo of their parent galaxies, it may exhibit missing mass in the form of dark baryons, unaccounted for by classical observations, as recently found in the collisional ring of NGC 5291 (Bournaud et al., 2007) and probably in the TDG VCC 2062. These "Lost Baryons" must originally have been located in the disks of their parent galaxies.

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arXiv2006

Intergalactic Star Formation

Star formation in interacting systems may take place in various locations, from the dust--enshrouded core of Ultraluminous Infrared Galaxies to more unusual places such as the debris of colliding galaxies expelled into the intergalactic medium. Determining whether star-formation proceeds in the latter environment, far from the parent galaxies, in a similar way as in spiral disks has motivated the multi--wavelength study presented here. We collected VLA/HI, UV/GALEX, optical Halpha and MIR/Spitzer images of a few nearby interacting systems chosen for their prominent "intergalactic" star formation activity. Preliminary results on the spectacular collisional HI ring around NGC 5291 are presented.

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arXiv2006

IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission

IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologically peculiar region of star formation in the western arm of NGC 2207. This clump, which dominates the Halpha and radio continuum emission from both galaxies, accounts for ~12% of the total 24mu m flux. Nearly half of the clumps are regularly spaced along some filamentary structure, whether in the starburst oval of IC 2163 or in the thin spiral arms of NGC 2207. This regularity appears to influence the clump luminosity function, making it peaked at a value nearly a factor of 10 above the completeness limit, particularly in the starburst oval. This is unlike the optical clusters inside the clumps, which have a luminosity function consistent with the usual power law form. The giant IR clumps presumably formed by gravitational instabilities in the compressed gas of the oval and the spiral arms, whereas the individual clusters formed by more chaotic processes, such as turbulence compression, inside these larger-scale structures.

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arXiv2005

The grazing encounter between IC 2163 and NGC 2207: Pushing the limits of observational modeling

We present numerical hydrodynamical models of the collision between the galaxies IC 2163 and NGC 2207. These models extend the results of earlier work where the galaxy discs were modeled one at a time. We confirm the general result that the collision is primarily planar, that is, at moderate inclination relative to the two discs, and prograde for IC 2163, but retrograde for NGC 2207. We list 34 specific morphological or kinematic features on a variety of scales, found with multi-waveband observations, which we use to constrain the models. The models are able to reproduce most of these features, with a relative orbit in which the companion (IC 2163) disc first side-swipes the primary (NGC 2207) disc on the west side, then moves around the edge of the primary disc to the north and to its current position on the east side. The models also provide evidence that the dark matter halo of NGC 2207 has only moderate extent. For IC 2163, the prolonged prograde disturbance in the model produces a tidal tail, and an oval or ocular waveform very much like the observed ones, including some fine structure. The retrograde disturbance in the model produces no strong waveforms within the primary galaxy. This suggests that the prominent spiral waves in NGC 2207 were present before the collision, and models with waves imposed in the initial conditions confirm that they would not be disrupted by the collision. With an initial central hole in the gas disc of the primary, and imposed spirals, the model also reproduces the broad ring seen in HI observations. We believe that this is now one of the best modeled systems of colliding galaxies. (Abridged)

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arXiv2005

A Chandra X-ray survey of nearby dwarf starburst galaxies: I. Data reduction and results

(abridged) We present an analysis of Chandra X-ray observations of a sample of eight dwarf starburst galaxies (I Zw 18, VII Zw 403, NGC 1569, NGC 3077, NGC 4214, NGC 4449, NGC 5253, and He 2-10). Extended, diffuse X-ray emission is detected in all but two of the objects. Unresolved sources were found within all dwarf galaxies (total: 55 sources). These point sources are well fit by power law, thermal plasma, or black body models. Ten of the point sources exceed an X-ray luminosity of 10^39 erg s^-1 (ultraluminous X-ray sources). In those galaxies where diffuse X-ray emission is detected, this emission (with X-ray luminosities ranging from 4x10^38 erg s^-1 to 2x10^40 erg s^-1) contains most (60-80 per cent) of the X-ray photons. This diffuse emission can be well fit by MeKaL one-temperature thermal plasma models once the contribution from the unresolved point sources is subtracted properly. The diffuse X-ray component is significantly extended, reaching as far as 0.5-5 kpc into the outskirts of their hosts. Temperatures of various regions within the galaxies range from 1.6-7.6x10^6 K. With few exceptions, temperatures of the hot gas are remarkably uniform, hovering around 2-3x10^6 K. Temperatures of the coronal gas in the outer regions are in general ~2-3 times lower than those found in the central regions. Fits to the diffuse emission do not allow strong constraints to be put on the metallicities of the emitting plasmas. However, the derived metallicities are compatible with those determined from their HII regions. An alpha/Fe ratio of ~2 is indicated for the hot gas within at least three objects (NGC 1569, NGC 4449, and He 2-10).

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arXiv2005

A Chandra X-ray survey of nearby dwarf starburst galaxies: II. Starburst properties and outflows

(abridged) We present a comprehensive comparison of the X-ray properties of a sample of eight dwarf starburst galaxies observed with Chandra (I Zw 18, VII Zw 403, NGC 1569, NGC 3077, NGC 4214, NGC 4449, NGC 5253, He 2-10). In Paper I we presented in detail the data reduction and analysis of the individual galaxies. For the unresolved X-ray sources we find the following: point sources are in general located close to bright HII regions, rims of superbubbles, or young stellar clusters. The number of X-ray point sources appears to be a function of the current star formation rate and the blue luminosity of the hosts. Ultraluminous X-ray sources are only found in those dwarf galaxies which are currently interacting. The power law index of the combined cumulative X-ray point source luminosity function is alpha=0.24+/-0.06, shallower than that of more massive starburst galaxies (alpha=0.4-0.8) and of non-starburst galaxies (alpha~1.2). For those galaxies showing extended X-ray emission (6 out of the 8 galaxies), we derive the following: Superwinds develop along the steepest gradient of the HI distribution with volume densities of 0.02-0.06 cm^-3, pressures of 1-3x10^5 K cm^-3, thermal energies of 2-30x10^54 erg, and hot gas masses of 2-20x10^6 Mo (~1 per cent of the HI masses). The mechanical luminosities of the developing superwinds are energetic enough to overcome the gravitational potentials of their host galaxies. This scenario is supported by the overpressures of the hot gas compared to the ambient ISM. Extended HI envelopes such as tidal tails, however, may delay outflows on timescales exceeding those of the cooling time of the hot gas.

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arXiv2004

The relation between galaxy activity and the dynamics of compact groups of galaxies

Using a sample of 91 galaxies distributed over 27 Compact Groups of Galaxies (CGs), we define an index that allows us to quantify their level of activity, be it AGN or star formation. By combining the mean activity index with the mean morphological type of the galaxies in a group we are able to quantify the evolutionary state of the groups. We find that they span a sequence in evolution, which is correlated with the spatial configuration of the galaxies making up a CG. We distinguish three main configuration: Type A CGs show predominantly low velocity dispersions and are rich in late-type spirals that are active in terms of star formation or harbor an AGN; Type B groups have intermediate velocity dispersions and contain a large fraction of interacting or merging galaxies; Type C is formed by CGs with high velocity dispersions, which are dominated by elliptical galaxies that show no activity. We suggest that the level of evolution increases in the sense A-->B-->C. Mapping the groups with different evolution levels in a diagram of radius versus velocity dispersion does not reveal the pattern expected based on the conventional fast merger model for CGs. Instead, we observe a trend that goes contrary to expectation: the level of evolution of a group increases with velocity dispersion. This trend seems to be related to the masses of the structures in which CGs are embedded. In general, the level of evolution of a group increases with the mass of the structure. This suggests either that galaxies evolve more rapidly in massive structures or that the formation of CGs embedded in massive structures predated the formation of CGs associated with lower mass systems. Our observations are consistent with CDM (or Lambda CDM) structures formation scenarios, assuming the formation of galaxies is a biased process.

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arXiv2004

VLA HI and OVRO CO Interferometry of a Tidal Dwarf Galaxy

We present high resolution interferometric observations of the cool atomic and cold molecular ISM of the TDG candidate Arp 245N, an object resembling a dwarf galaxy in the northern tidal tail of the interacting system NGC 2992/3. We observed the HI line with the NRAO VLA and the CO(1-->0) transition with the OVRO millimeter interferometer at 5''-6'' angular resolution (750 pc linear resolution). These datacubes offer the required spatial and velocity resolution to determine whether the mass concentration near the tip of the tail is a genuine feature, and hence a good TDG candidate, or an artefact caused by a fortuitous alignment of our line of sight with the direction of the tail. A preliminary analysis seems to confirm that Arp 245N is a self-gravitating entity.

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arXiv2002

Molecular gas in the intergalactic medium of Stephan's Quintet

Stephan's Quintet (SQ) is a Hickson Compact Group well known for its complex dynamical and star formation history and its rich intergalactic medium (IGM). In order to study the extent, origin and fate of the intergalactic molecular gas and its relation to the formation of stars outside galaxies and Tidal Dwarf Galaxies (TDGs), we mapped with the IRAM 30m antenna carbon monoxide (CO) towards several regions of the IGM in SQ. In two star forming regions (SQ A and B), situated in very different environments, we detected unusually large amounts of molecular gas ($3.1 \times 10^9$ \msun and $7 \times 10^8$ \msun, respectively), covering an extended area (between 15 and 25 kpc). In both regions the CO clouds have different properties and may be of a distinct nature. The integrated CO line of SQ A is in particular much wider than in SQ B. Its CO spectrum shows emission at two velocities (6000 and 6700 \kms), coincident with two HI lines, with the stronger emission at 6000 \kms being very smoothly distributed without a distinct peak in the starburst region. In SQ B the CO emission coincides with that of tracers of star formation (\halpha, near-infrared 15 $μ$m and radio continuum). The CO peak lies close to the HI peak towards a steep HI gradient. This is indicating that the molecular gas is forming in-situ, with subsequent star formation taking place. The star forming region at SQ B is the object in SQ that most resembles a TDG.

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arXiv2002

Abundant molecular gas in the intergalactic medium of Stephan's Quintet

Stephan's Quintet (SQ) is a system consisting of at least four interacting galaxies which is well known for its complex dynamical and star formation history. It possesses a rich intergalactic medium (IGM), where hydrogen clouds, both atomic and molecular, associated with two starbursts (refered to as SQ A and B) have been found. In order to study the extent, origin and fate of the intergalactic molecular gas and its relation to the formation of stars outside galaxies and Tidal Dwarf Galaxies (TDGs), we mapped with the IRAM 30m antenna the carbon monoxide (CO) towards several regions of the IGM in SQ. In both SQ A and B, we detected unusually large amounts of molecular gas (3.1 times 10^9 msun and 7 times 10^8 msun, respectively). In contrast, no significant CO detection was achieved towards HII regions south of the pair NGC 7318a/b despite their high H alpha luminosities. The molecular gas is very extended in both SQ A and SQ B, over areas of between 15 and 25 kpc. The CO clouds seem to have otherwise different properties and may be of a different nature. The integrated CO line of SQ A is in particular much wider than in SQ B. Its CO spectrum shows emission at two velocities (6000 and 6700 km s^{-1}) that are coincident with two HI lines. The strongest emission at 6000 km s^{-1} is however spatially offset from the HI emission and situated on a ridge south-east of the starburst region. In SQ B the CO emission coincides with that of tracers of star formation (halpha, 15 mu m and radio continuum). The CO peak lies slightly offset from the HI peak towards a steep HI gradient. This is indicating that the molecular gas is forming in-situ, possibly in a region of compressed HI, with subsequent star formation. The star forming region at SQ B is the object in SQ that most resembles a TDG.

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arXiv2002

ROSAT X-ray observations of the dwarf galaxy Holmberg II

We present a study of the irregular dwarf galaxy Holmberg II based on ROSAT PSPC observations (total exposure time: 22 ksec). Holmberg II is a nearby (3.2 Mpc), well-studied dwarf irregular galaxy. It is famous for its interstellar medium which is dominated by expanding structures such as HI holes and shells. We search for X-ray emission from point sources as well as for diffuse emission, down to the detection limit of the ROSAT data. Using X-ray hardness ratio diagrams we differentiate between thermal plasma and power-law X-ray spectra which helps to determine the nature of the individual sources. Correlating the X-ray data with complementary observations ranging from the far-ultraviolet to the radio regime we increase the probability of correctly identifying sources belonging to Holmberg II. We did not detect soft X-ray emission originating from hot gas within supergiant HI shells above our luminosity sensitivity limit of (L_limit(0.1 - 2.1 keV) ~ 10^{37}erg/s). This finding can probably be attributed to blow-out in the case of the largest holes and insufficient sensitivity (due to strong photoelectric absorption) in case of the smaller HI holes. However we find faint X-ray sources well beyond the stellar body but within the HI distribution of Holmberg II, which suggests the presence of X-ray binaries. This indicates that star formation has taken place across the entire gaseous disk of Holmberg II in the past, some of which may have created the structures seen in the ISM at large galactocentric radii.

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arXiv2001

Mass loss from galaxies: feeding the IGM, recycling in the IGM

As a result of internal processes or environmental effects like ram-pressure stripping or collisions, galaxies lose a significant part of their stellar and gaseous content. Whereas the impact of such stripping on galaxy evolution has been well studied, much less attention has been given to the fate of the expelled material in the intergalactic or intracluster medium (IGM/ICM). Observational evidence exists showing that a fraction of the injected matter is actually recycled to form a new generation of galaxies, such as the Tidal Dwarf Galaxies discovered near numerous interacting systems. Using a set of multiwavelength data, we are now able to roughly analyze the processes pertaining to their formation: from an instability in the HI clouds, through the formation of molecular gas, and to the onset of star formation.

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arXiv2001

CO Observations of the Interacting Galaxy Pair NGC 5394/95

BIMA CO 1-0 observations are presented of the spiral galaxies NGC 5394 and NGC 5395 that have undergone a recent, grazing encounter. In NGC 5394, 80% of the CO emission detected by BIMA is concentrated in the central 800 pc (FWHM) starburst region.In an encounter simulation that reproduces some of the main features of this galaxy pair, a considerable amount of gas in NGC 5394 falls into the central region early in the collision. The observed total gas distribution in the disk of NGC 5394 is lopsided, with more HI, CO, and H-alpha emission coming from the western or southwestern side. The innermost western arm of NGC 5394 is seen in CO and H-alpha emission, but the eastern inner-disk arm, which is very bright in the optical continuum, is not detected in CO or H-alpha emission. From a comparison of the radio continuum, H-alpha, 60 micron, and CO luminosities, we estimate that the average visual extinction of the starburst is 3 - 4 mag and the conversion factor N(H2)/I(CO) in the starburst is a factor of 3 - 4 below the standard value. Comparison of NGC 5394 with two other systems previously studied suggests that in prograde grazing encounters a central starburst may not develop until near the end of the ocular phase. Very little of the CO emission from NGC 5395 found in previous single-dish observations is detected by BIMA.

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arXiv2001

Evidence for Blow-out in the Low-mass Dwarf Galaxy Holmberg I

We present radio and optical observations of Holmberg I (HoI), a member of the M81 group of galaxies (distance 3.6Mpc). HoI is a low-mass, low surface- brightness dwarf galaxy. High-resolution multi-array VLA HI observations reveal a supergiant shell (diameter: 1.7 kpc) which covers about half the optical extent of HoI and which comprises 75% of the total HI content (total HI mass: 1.1 10^8 M_o). We set a tentative upper limit to the dark matter content of < 3.1 10^8 M_o. The HI data are complemented by deep, optical UBV(RI)_c and Halpha observations obtained at the Calar Alto 2.2m telescope. We find M_HI/L_B = 1.1 M_o/L_B_o. The total visible (stars plus gas) mass of HoI adds up to 2.4 10^8 M_o. This leads to a total mass of < 5.5 10^8 M_o. The origin of HoI's peculiar HI morphology is discussed in terms of a supergiant shell created by strong stellar winds and supernova explosions (energy: equiv. 20-260 type II SN; age: 80+-20 Myr). The morphological center of HoI is offset by 0.75 kpc with respect to the dynamical center. Within the interior of the shell the light distribution is exponential with a rather shallow gradient and blue optical colors. Beyond a radius corresponding to an HI column density of 10^21 cm^-2, the putative star formation (SF) threshold, the disk becomes considerably redder and the slope for the exponential light distribution steepens. It is speculated that a generation of stars (age 15-30 Myr) is the result of secondary SF on the rim of the shell. Based on the global morphology and velocity dispersion as well as the location of the HII regions we find evidence for ram pressure within the M81 group. Finally, we discuss the likelihood of HoI having lost some of its interstellar material to the intergalactic medium (''blow-out'' scenario).

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arXiv2001

21-cm H I emission from the Damped Lyman-alpha absorber SBS 1543+593

We detect 21-cm emission from the Low Surface Brightness (LSB) galaxy SBS 1543+593, which gives rise to a Damped Lyman-alpha (DLA) absorption line in the spectrum of the background QSO HS 1543+5921 (z=0.807). We obtain an accurate measure of the velocity of the H I gas in the LSB galaxy, v=2868 km/s, and derive a mass of 1.3e9 solar masses. We compare this value with limits obtained towards two other z~0.1 DLA systems, and show that SBS 1543+593 would not have been detected. Hence LSB galaxies similar to SBS 1543+593 can be responsible for DLA systems at even modest redshifts without being detectable from their 21-cm emission.

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arXiv2000

HI Recycling: Formation of Tidal Dwarf Galaxies

Galactic collisions trigger a number of phenomena, such as transportation inward of gas from distances of up to kiloparsecs from the center of a galaxy to the nuclear region, fuelling a central starburst or nuclear activity. The inverse process, the ejection of material into the intergalactic medium by tidal forces, is another important aspect and can be studied especially well through detailed HI observations of interacting systems which have shown that a large fraction of the gaseous component of colliding galaxies can be expelled. Part of this tidal debris might fall back, be dispersed throughout the intergalactic medium or recondense to form a new generation of galaxies: the so-called tidal dwarf galaxies. The latter are nearby examples of galaxies in formation. The properties of these recycled objects are reviewed here and different ways to identify them are reviewed.

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arXiv1999

Study of the interacting system NGC 6845

We present optical spectroscopy, B, V, R and I CCD photometry and VLA neutral hydrogen observations of the interacting quartet NGC 6845, also know as Klemola 30. NGC 6845 A, the dominant component, sports a broad and bright tidal bridge and a faint tidal tail, which bifurcate. The tidal bridge has a (B-I) color bluer than that of NGC 6845 A inner disk. Five strong condensations, identified as HII regions brighter than the brightest in our Galaxy, are found along the tidal bridge, with the two most luminous located at the bridge tip. Two giant HII regions, comparable to 30 Dor, are located where the tidal bridge and the tidal tail joint the disk of NGC 6845 A. Since the age of the HII regions are 3-8 Myr, star formation has been occurring along the tidal bridge and the tidal arm well after they had begun to be torn apart (>= 100 Myr). Satoh model fitting to the rotation curve of the A component reveals a kinematical mass of 4.4(+-1.2)E11 M_sun, inside the central 12 kpc (H_0=75 km/s/Mpc). The HI emission shows two components, a more massive one that belongs to NGC 6845 A, and a second one associated to NGC 6845 B. We do not detect gas associated to galaxies C and D. The total amount of HI is 1.4E10 M_sun, five time the HI content of the Milky Way. The HI kinematics indicates an amount of dark matter associated to the A component two times higher than the mass inside its central 12 kpc. The group kinematics indicates an M/L ~ 43(+-2) or M/L ~ 66(+-2) (solar units), according to two different prescriptions for the internal absorption correction. In spite of this difference, both values furnish similar group mass (~1E13 M_sun). Although preliminary results on N-Body simulations indicate that either B or C might well create a tidal feature like the bridge of the A component, the collision with B appears to be more favourable.

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