arXiv subjects

Jeffrey D. P. Kenney

Publications and source records attributed to Jeffrey D. P. Kenney.

46 records · Page 3Linked to original sources

arXiv2002

Molecular Gas in The Central Kpc of Starbursts and AGN

With the recent advent of large interferometric surveys, we can now probe the physical conditions, dynamics, and star-forming properties of molecular gas in the central kpc of starbursts and active galactic nuclei. We present results from the high-resolution (~ 100 pc) interferometric survey of molecular gas in the inner kpc of nearby starbursts (Jogee, Kenney, and Scoville 2001a) and the ongoing multi-transition survey of cold, warm, and dense molecular gas in a broad range of active and inactive galactic nuclei (Jogee, Baker, Sakamoto, and Scoville 2001b).

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arXiv2001

Hubble Space Telescope Imaging of Bipolar Nuclear Shells in the Disturbed Virgo Cluster Galaxy NGC 4438

We present broadband and narrowband Hubble Space Telescope images of the central region of the heavily disturbed Virgo cluster galaxy NGC 4438 (Arp120), whose nucleus has been described as a type 1 LINER or dwarf Seyfert. Narrowband H-alpha and [NII] HST images reveal striking bipolar shell features, 1 kpc in projected length from end-to-end, which are likely the result of an outflow from the nuclear region experiencing a strong interaction with the ISM. While these outflow shells share similarities with those in some other starburst or AGN galaxies, these in NGC 4438 are notable because NGC 4438 harbors neither a luminous circumnuclear starburst nor a luminous AGN. The shells appear to be closed at their outer ends, suggesting that the outflow in NGC 4438 is dynamically younger than those in some other galaxies. The radio continuum emission is strongly enhanced near the outer ends of the shells, suggesting working surfaces arising from collimated nuclear outflows which have impacted and shocked the surrounding ISM. The 2 shells are quite different, as the northwestern (NW) shell is luminous and compact, while the southeastern (SE) shell is 2.5 times longer and much fainter, in both optical emission lines and the non-thermal radio continuum. The differences between the 2 shells may be attributed to a difference in ISM density on the 2 sides of the nuclear disk. Such an ISM asymmetry exists on larger scales in this heavily disturbed galaxy. At the base of the outflow is a nuclear source, which is the highest surface brightness source in the galaxy at optical wavelengths, We discuss whether the outflow is powered by a low luminosity AGN or a compact nuclear starburst.

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arXiv2001

NGC 4314. IV. Photometry of Star Clusters with Hubble Space Telescope - History of Star Formation in the Vicinity of a Nuclear Ring

Using HST WFPC2 images, we have obtained U, B, V, I, and H-alpha photometry for 76 star clusters in the nuclear star-forming ring of the barred spiral galaxy NGC 4314. These clusters are likely associated with an inner Inner Lindblad Resonance, or IILR. The blue colors and H-alpha emission for most of these clusters imply very young ages of 1-15 Myr. Age estimates based on several reddening-free parameters indicate that the present epoch of star formation has lasted at least 30 Myr. By estimating the masses of stars in the clusters and comparing with the H-alpha luminosity, we conclude that a significant fraction of ongoing star formation in the nuclear ring of NGC 4314 occurs in clusters. The cluster masses identify these as young open clusters, not young globular clusters. Further out in the galaxy, just exterior to the ring of young stars, previous ground-based observations revealed two symmetric stellar spiral arms which may be associated with an outer Inner Lindblad Resonance, or OILR. With our HST data, we have revealed part of this structure and its colors in more detail. The spiral arm colors are consistent with stellar ages between 40 and 200 Myr. The age difference between the inner ring of young stars (IILR) and the larger oval-like feature containing the blue arms (OILR) supports an interpretation of the morphology of the nuclear region of NGC 4314 that requires a reservoir of gas that becomes more compact over time. We speculate that as the gas distribution becomes more centrally concentrated, it interacts with these two resonances. Each resonance triggers star formation, resulting in two distinct epochs of star formation.

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arXiv1999

A gas-rich nuclear bar fuelling a powerful central starburst in NGC 2782

We present evidence that the peculiar interacting starburst galaxy NGC 2782 (Arp 215) harbors a gas-rich nuclear stellar bar feeding an M82-class powerful central starburst, from a study based on OVRO CO (J=1->0) data, WIYN BVR & Halpha observations, along with available NIR images, a 5 GHz RC map and HST images. NGC 2782 harbors a clumpy, bar-like CO feature of radius ~ 7.5'' (1.3 kpc) which leads a nuclear stellar bar of similar size. The nuclear CO bar is massive: it contains ~2.5x10**9 M_sun of molecular gas, which makes up ~ 8 % of the dynamical'mass present within a 1.3 kpc radius. Within the CO bar, emission peaks in two extended clumpy lobes which lie on opposite sides of the nucleus, separated by ~ 6'' (1 kpc). Between the CO lobes, in the inner 200 pc radius, resides a powerful central starburst which is forming stars at a rate of 3 to 6 M_sun yr-1. While circular motions dominate the CO velocity field, the CO lobes show weak bar-like streaming motions on the leading side of the nuclear stellar bar, suggestive of gas inflow. We estimate semi-analytically the gravitational torque from the nuclear stellar bar on the gas, and suggest large gas inflow rates from the CO lobes into the central starburst. These observations, which are amongst the first ones showing a nuclear stellar bar fuelling molecular gas into an intense central starburst, are consistent with simulations and theory which suggest that nuclear bars provide an efficient way of transporting gas closer to the galactic center to fuel central activity. Furthermore, several massive clumps are present at low radii, and dynamical friction might produce further gas inflow. We suggest that the nuclear molecular gas bas and central activity will be very short-lived, likely disappearing within 5x10**8 years.

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arXiv1999

Kinematic Disturbances in Optical Rotation Curves among 89 Virgo Disk Galaxies

For 89 galaxies, mostly spirals, in the Virgo cluster region, we have obtained optical long-slit major axis spectra of the ionized gas. We find: (1) One-half of the Virgo galaxies we observed have regular rotation patterns, while the other 50% exhibit kinematic disturbances ranging from mild to major. Velocity complexities are generally consistent with those resulting from tidal encounters or accretion events. Since kinematic disturbances are expected to fade within ~10^9 years, many Virgo galaxies have experienced several significant kinematic disturbances during their lifetimes. (2) A few Virgo galaxies have ionized gas of limited extent, with velocities exceptionally low for their luminosities. In these galaxies the gas must be not rotationally supported. (3) There is a remarkable difference in the distribution of galaxy systemic velocity for galaxies with Regular rotation curves and galaxies with Disturbed rotation curves. Galaxies with regular rotation patterns show a flat distribution with systemic velocity, while galaxies with disturbed kinematics have a Gaussian distribution very similar to that for the elliptical galaxies in Virgo. This suggests that spirals with disturbed kinematics are preferentially on radial orbits, which bring them to the cluster core, where tidal interactions are strong and/or more common. These interactions may alter the morphology of the galaxy, and may also play a role in driving the Virgo cluster toward dynamical equilibrium.

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arXiv1998

Ongoing Gas Stripping in the Virgo Cluster Spiral NGC 4522

The Virgo cluster galaxy NGC 4522 is one of the best spiral candidates for ICM-ISM stripping in action. Optical broadband and H-alpha images from the WIYN telescope of the highly inclined galaxy reveal a relatively undisturbed stellar disk and a peculiar distribution of H-alpha emission. Ten percent of the H-alpha emission arises from extraplanar HII regions which appear to lie within filamentary structures >3 kpc long above one side of the disk. The filaments emerge from the outer edge of a disk of bright H-alpha emission which is abruptly truncated beyond 0.35R(25). Together the truncated H-alpha disk and extraplanar H-alpha filaments are reminiscent of a bow shock morphology, which strongly suggests that the interstellar medium (ISM) of NGC 4522 is being stripped by the gas pressure of the intracluster medium (ICM). The galaxy has a line-of-sight velocity of 1300 km/sec with respect to the mean Virgo cluster velocity, and thus is expected to experience a strong interaction with the intracluster gas. The existence of HII regions apparently located above the disk plane suggests that star formation is occuring in the stripped gas, and that newly formed stars will enter the galaxy halo and/or intracluster space. The absence of HII regions in the disk beyond 0.35R(25), and the existence of HII regions in the stripped gas suggest that even molecular gas has been effectively removed from the disk of the galaxy.

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arXiv1998

The Molecule-Rich Tail of the Peculiar Galaxy NGC 2782 (Arp 215)

We present the first detection of a large quantity of molecular gas in the extended tail of an interacting galaxy. Using the NRAO 12m telescope, we have detected CO (1 - 0) at five locations in the eastern tail of the peculiar starburst galaxy NGC 2782. The CO velocities and narrow (FWHM = 50 km/s) line widths in these positions agree with those seen in HI, confirming that the molecular gas is indeed associated with the tail rather than the main disk. As noted previously, the gas in this tail has an apparent `counter-rotation' compared to gas in the core of the galaxy, probably because the tails do not lie in the same plane as the disk. Assuming the standard Galactic conversion N(H2)/I(CO) factor, these observations indicate a total molecular gas mass of 6 X 10**8 M(sun) in this tail. This may be an underestimate of the total H2 mass if the gas is metal-poor. This molecular gas mass, and the implied H2/HI mass ratio of 0.6, are higher than that found in many dwarf irregular galaxies. Comparison with an available H-alpha map of this galaxy, however, shows that the rate of star formation in this feature is extremely low relative to the available molecular gas, compared to L(H-alpha)/M(H2) values for both spiral and irregular galaxies. Thus the timescale for depletion of the gas in this feature is very long.

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arXiv1997

The remarkable starburst-driven outflow in NGC 2782

We show that the starburst-driven outflow in the peculiar galaxy NGC 2782 forms a well-defined collimated bubble which has an extent of $\sim$ 1 kpc and a closed shell at its edge, as seen in H$α$, [O III], and 5 GHz radio continuum. The shell coincides with the maximum in intensity and linewidths of [O III] lines in a blueshifted emission nebula which was previously detected via optical spectroscopy by Boer et al. (1992). Such a remarkable outflow morphology has not been observed to date in any other starburst galaxy of comparable luminosity. The radio continuum map reveals a second bubble of similar size on the opposite side of the nucleus, forming a striking double-bubble outflow morphology. We argue from the morphology and short timescale ($\sim$ $4 \times 10^6$ years) of the outflow that it is dynamically younger than freely-expanding outflows seen in other galaxies which harbor circumnuclear starbursts of comparable luminosity, e.g., M82. We suggest that the outflow in NGC 2782 is in the early stage where thermal instabilities have not yet completely ruptured the outflow bubble.We present evidence that the outflow is driving warm and hot ionised gas, and possibly cold molecular gas, out of the central kpc of the galaxy. We estimate the contribution of the hot, warm, and cold phases of the ISM to the energetics of the outflow. This study is based on our optical BVR, H$α$, and [O III] observations from the WIYN telescope and OVRO CO interferometric data, along with available 5 GHz radio continuum and ROSAT X-ray maps.

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arXiv1996

NGC 4314. III. Inflowing Molecular Gas Feeding a Nuclear Ring of Star Formation

NGC 4314 is an early-type barred galaxy containing a nuclear ring of recent star formation. We present CO(1-0) interferometer data of the bar and circumnuclear region with 2.3 x 2.2 arcsec spatial resolution and 13 km/s velocity resolution acquired at the Owens Valley Radio Observatory . These data reveal a clumpy circumnuclear ring of molecular gas. We also find a peak of CO inside the ring within 2 arcsec of the optical center that is not associated with massive star formation. We construct a rotation curve from these CO kinematic data and the mass model of Combes et al. (1992). Using this rotation curve, we have identified the location of orbital resonances in the galaxy. Assuming that the bar ends at corotation, the circumnuclear ring of star formation lies between two Inner Lindblad Resonances, while the nuclear stellar bar ends near the IILR. Deviations from circular motion are detected just beyond the CO and H-alpha ring, where the dust lanes along the leading edge of the bar intersect the nuclear ring. These non-circular motions along the minor axis correspond to radially inward streaming motions at speeds of 20 - 90 km/s and clearly show inflowing gas feeding an ILR ring. There are bright HII regions near the ends of this inflow region, perhaps indicating triggering of star formation by the inflow.

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arXiv1994

An Estimate of the Gas Inflow Rate Along the Bar in NGC 7479

We present images of the barred galaxy NGC 7479 in the optical and near infrared broad--bands $B,V,R,J,H,K$, and images in H$α$+[N II] and CO(J=1$\rightarrow$0) emission. The H$α$ and CO emission in the bar are coincident and confined to narrow linear features that are offset from the center of the bar as observed in the near infrared. We estimate the gravitational potential from the $K$ image, which provides an estimate of the torque on the gas at the position of the CO emission in the bar. We find that the implied gas inflow velocity derived from the torque is $10-20$ km s$^{-1}$. Our inflow velocity is independent of the large streaming motions which can be observed in CO and HI.

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