arXiv subjects

M. E. Putman

Publications and source records attributed to M. E. Putman.

At least 55 records · Page 3Linked to original sources

arXiv2006

Potential Condensed Fuel for the Milky Way

Potential condensed clouds of gas in the Galactic halo are examined in the context of the recent models of cooling, fragmenting clouds building up the baryonic mass of the Galaxy. 582 high-velocity clouds (HVCs) are defined as the potential infalling, condensed clouds and the sample's spatial and velocity distribution are presented. With the majority of the hydrogen in the clouds ionized (~85%), the clouds at a distribution of distances within 150 kpc, and their individual total masses below 10^7 Msun, the total mass in potentially condensed clouds is 1.1 - 1.4 x 10^9 Msun. If the tighter distance constraint of < 60 kpc is adopted this mass range drops to 4.5 - 6.1 x 10^8 Msun. The implications on the condensing cloud models, as well as feedback and additional accretion methods, are discussed.

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arXiv2006

The Galactic Nature of High Velocity Cloud Complex WB

We have detected absorption lines from the High Velocity Cloud Complex WB in the spectrum of the star HE1048+0231. This detection sets an upper distance limit to the cloud of 8.8^{+2.3}_{-1.3} kpc. Non-detection (at >4 sigma confidence) in the star HE1138-1303 at 7.7 +/- 0.2 kpc sets a probable lower limit. The equivalent width of the CaII K line due to the HVC (114.6 +/- 4.4 mA) corresponds to a column density of 1.32 +/- 0.05 x 10^12 cm^-2. Using an HI spectrum from the Leiden/Argentine/Bonn survey, we calculated N(CaII)/N(HI) = 81 +/- 16 x 10^-9. These distance limits imply an HI mass limit of 3.8 x 10^5 Msun < M_HI < 4.9 x 10^5 Msun. The upper distance limit imposed by these observations shows that this HVC complex has a probable Galactic or circum-Galactic origin. Future metallicity measurements will be able to confirm or refute this interpretation.

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arXiv2005

The Relationship Between Baryons and Dark Matter in Extended Galaxy Halos

The relationship between gas-rich galaxies and Ly-alpha absorbers is addressed in this paper in the context of the baryonic content of galaxy halos. Deep Arecibo HI observations are presented of two gas-rich spiral galaxies within 125 kpc projected distance of a Ly-alpha absorber at a similar velocity. The galaxies investigated are close to edge-on and the absorbers lie almost along their major axes, allowing for a comparison of the Ly-alpha absorber velocities with galactic rotation. This comparison is used to examine whether the absorbers are diffuse gas rotating with the galaxies' halos, outflow material from the galaxies, or intergalactic gas in the low redshift cosmic web. The results indicate that if the gas resides in the galaxies' halos it is not rotating with the system and possibly counter-rotating. In addition, simple geometry indicates the gas was not ejected from the galaxies and there are no gas-rich satellites detected down to 3.6 - 7.5 x 10^6 Msun, or remnants of satellites to 5-6 x 10^{18} cm^{-2}. The gas could potentially be infalling from large radii, but the velocities and distances are rather high compared to the high velocity clouds around the Milky Way. The most likely explanation is the galaxies and absorbers are not directly associated, despite the vicinity of the spiral galaxies to the absorbers (58-77 kpc from the HI edge). The spiral galaxies reside in a filament of intergalactic gas, and the gas detected by the absorber has not yet come into equilibrium with the galaxy. These results also indicate that the massive, extended dark matter halos of spiral galaxies do not commonly have an associated diffuse baryonic component at large radii.

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arXiv2005

The HIPASS Catalogue: III - Optical Counterparts & Isolated Dark Galaxies

We present the largest catalogue to date of optical counterparts for HI radio-selected galaxies, Hopcat. Of the 4315 HI radio-detected sources from the HI Parkes All Sky Survey (Hipass) catalogue, we find optical counterparts for 3618 (84%) galaxies. Of these, 1798 (42%) have confirmed optical velocities and 848 (20%) are single matches without confirmed velocities. Some galaxy matches are members of galaxy groups. From these multiple galaxy matches, 714 (16%) have confirmed optical velocities and a further 258 (6%) galaxies are without confirmed velocities. For 481 (11%), multiple galaxies are present but no single optical counterpart can be chosen and 216 (5%) have no obvious optical galaxy present. Most of these 'blank fields' are in crowded fields along the Galactic plane or have high extinctions. Isolated 'Dark galaxy' candidates are investigated using an extinction cut of ABj < 1 mag and the blank fields category. Of the 3692 galaxies with an ABj extinction < 1 mag, only 13 are also blank fields. Of these, 12 are eliminated either with follow-up Parkes observations or are in crowded fields. The remaining one has a low surface brightness optical counterpart. Hence, no isolated optically dark galaxies have been found within the limits of the Hipass survey.

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arXiv2004

The Parkes HI Survey of the Magellanic System

We present the first fully and uniformly sampled, spatially complete HI survey of the entire Magellanic System with high velocity resolution, performed with the Parkes Telescope. The final data-cubes have an rms noise of sigma ~ 0.05 K and an effective angular resolution of 16 arcmin. The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are associated with huge gaseous features with a total HI mass of M(HI) = 4.87 10^8 M_sun [d/55 kpc]^2, if all HI gas is at the same distance of 55 kpc. Approximately two thirds of this HI gas is located close to the Magellanic Clouds (Magellanic Bridge and Interface Region), and 25% of the HI gas is associated with the Magellanic Stream. The Leading Arm has a four times lower HI mass than the Magellanic Stream, corresponding to 6% of the total HI mass of the gaseous features. We have analyzed the velocity field of the Magellanic Clouds and their neighborhood introducing a LMC-standard-of-rest frame. The HI in the Magellanic Bridge shows low velocities relative to the Magellanic Clouds suggesting an almost parallel motion, while the gas in the Interface Region has significantly higher relative velocities indicating that this gas is leaving the Magellanic Bridge building up a new section of the Magellanic Stream. The clouds in the Magellanic Stream and the Leading Arm show significant differences, both in the column density distribution and in the shapes of the line profiles. The HI gas in the Magellanic Stream is more smoothly distributed than the gas in the Leading Arm. These morphological differences can be explained if the Leading Arm is at considerably lower z-heights and embedded in a higher pressure ambient medium.

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arXiv2004

The Gaseous Trail of the Sagittarius Dwarf Galaxy

A possible gaseous component to the stream of debris from the Sagittarius dwarf galaxy is presented. We identify 4 - 10 x 10^6 Msun of neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic anticenter (at 36 kpc, the distance to the stellar debris in this region). This is 1-2% of the estimated total mass of the Sgr dwarf. Both the stellar and gaseous components have negative velocities, but the gaseous component extends to higher negative velocities. If associated, this gaseous stream was most likely stripped from the main body of the dwarf 0.2 - 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10^{-4} cm^{-3}. This gas represents the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.

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arXiv2003

Intergalactic HII Regions Discovered in SINGG

A number of very small isolated HII regions have been discovered at projected distances up to 30 kpc from their nearest galaxy. These HII regions appear as tiny emission line objects in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic confirmation of four isolated HII regions in two systems, both systems have tidal HI features. The results are consistent with stars forming in interactive debris due to cloud-cloud collisions. The H-alpha luminosities of the isolated HII regions are equivalent to the ionizing flux of only a few O stars each. They are most likely ionized by stars formed in situ, and represent atypical star formation in the low density environment of the outer parts of galaxies. A small but finite intergalactic star formation rate will enrich and ionize the surrounding medium. In one system, NGC 1533, we calculate a star formation rate of 1.5e-3 msun/yr, resulting in a metal enrichment of ~1e-3 solar for the continuous formation of stars. Such systems may have been more common in the past and a similar enrichment level is measured for the `metallicity floor' in damped Lyman-alpha absorption systems.

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arXiv2003

The Galaxy's Eating Habits

The possibility of a gaseous halo stream which was stripped from the Sagittarius dwarf galaxy is presented. The total mass of the neutral hydrogen along the orbit of the Sgr dwarf in the direction of the Galactic anticenter is 4-10 x 10^6 Msun (at 36 kpc, the distance to the stellar debris in this region). Both the stellar and gaseous components have negative velocities in this part of the sky, but the gaseous component extends to higher negative velocities. We suggest this gaseous stream was stripped from the main body of the dwarf 0.2 - 0.3 Gyr ago during its current orbit after a passage through a diffuse edge of the Galactic disk with a density > 10^{-4} cm^{-3}. The gas would then represent the dwarf's last source of star formation fuel and explains how the galaxy was forming stars 0.5-2 Gyr ago.

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arXiv2003

Discovery of Intergalactic HII Regions

We have discovered a number of very small isolated HII regions 20-30 kpc from their nearest galaxy. The HII regions appear as tiny emission line dots (ELdots) in narrow band images obtained by the NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG). We have spectroscopic confirmation of 5 isolated HII regions in 3 systems. The H-alpha luminosities of the HII regions are equivalent to the ionizing flux of only 1 large or a few small OB stars each. These stars appear to have formed in situ and represent atypical star formation in the low density environment of galaxy outskirts. In situ star formation in the intergalactic medium offers an alternative to galactic wind models to explain metal enrichment. In interacting systems (2 out of 3), isolated HII regions could be a starting point for tidal dwarf galaxies.

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arXiv2003

H_alpha Emission from High-Velocity Clouds and their Distances

We present deep Halpha spectroscopy towards several high-velocity clouds (HVCs) which vary in structure from compact (CHVCs) to the Magellanic Stream. The clouds range from being bright (~640 mR) to having upper limits on the order of 30 to 70 mR. The Halpha measurements are discussed in relation to their HI properties and distance constraints are given to each of the complexes based on f_esc = 6% of the ionizing photons escaping normal to the Galactic disk (f_escs = 1 - 2% when averaged over solid angle). The results suggest that many HVCs and CHVCs are within a ~40 kpc radius from the Galaxy and are not members of the Local Group at megaparsec distances. However, the Magellanic Stream is inconsistent with this model and needs to be explained. It has bright Halpha emission and little [NII] emission and appears to fall into a different category than the currently detected HVCs. This may reflect the lower metallicities of the Magellanic Clouds compared to the Galaxy, but the strength of the Halpha emission cannot be explained solely by photoionization from the Galaxy. The interaction of the Stream with halo gas or the presence of yet unassociated young stars may assist in ionizing the Stream.

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arXiv2003

The 1000 Brightest HIPASS Galaxies: HI Mass Function and Omega_HI

We present a new accurate measurement of the HI mass function of galaxies from the HIPASS Bright Galaxy Catalog, a sample of 1000 galaxies with the highest HI peak flux densities in the southern hemisphere (Koribalski et al. 2003). This sample spans nearly four orders of magnitude in HI mass (from log M_HI/M_sun=6.8 to 10.6, H0=75) and is the largest sample of HI selected galaxies to date. We develop a bivariate maximum likelihood technique to measure the space density of galaxies, and show that this is a robust method, insensitive to the effects of large scale structure. The resulting HI mass function can be fitted satisfactorily with a Schechter function with faint-end slope alpha=-1.30. This slope is found to be dependent on morphological type, with later type galaxies giving steeper slopes. We extensively test various effects that potentially bias the determination of the HI mass function, including peculiar motions of galaxies, large scale structure, selection bias, and inclination effects, and quantify these biases. The large sample of galaxies enables an accurate measurement of the cosmological mass density of neutral gas: Omega_HI=(3.8 +/- 0.6) x 10^{-4}. Low surface brightness galaxies contribute only 15% to this value, consistent with previous findings.

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arXiv2002

The Large Scale Distribution of Neutral Hydrogen in the Fornax Region

Using HIPASS data, we have searched for HI in a ~25x25 sq.deg. region centred on the Fornax cluster. Within a velocity search range of 300 - 3700 km/s and a lower flux limit of ~40 mJy, 110 galaxies with HI emission were detected, one of which is previously uncatalogued. None of the detections has early-type morphology. Previously unknown velocities for 14 galaxies have been determined, with a further 4 velocity measurements being significantly dissimilar to published values. Identification of an optical counterpart is relatively unambiguous for more than ~90% of our HI galaxies. The galaxies appear to be embedded in a sheet at the cluster velocity which extends for more than 30 deg across the search area. At the nominal cluster distance of ~20 Mpc, this corresponds to an elongated structure more than 10 Mpc in extent. A velocity gradient across the structure is detected, with radial velocities increasing by \~500 km/s from SE to NW. The clustering of galaxies evident in optical surveys is only weakly suggested in the spatial distribution of our HI detections. Our results suggest a considerable deficit of HI-rich galaxies in the centre of the cluster. However, relative to the field, there is a 3(+/-1)-fold excess of HI-rich galaxies in the outer parts of the cluster where galaxies may be infalling towards the cluster for the first time.

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arXiv2002

The Magellanic Stream, High-Velocity Clouds and the Sculptor Group

The Magellanic Stream is a 100°x 10°filament of gas which lies within the Galactic halo and contains ~ 2 x 10^8 \Msun of neutral hydrogen. We present data from the HI Parkes All Sky Survey (HIPASS) in the first complete survey of the entire Magellanic Stream and its surroundings. We also present a summary of the reprocessing techniques used to recover large-scale structure in the Stream. The Stream properties revealed include: bifurcation along the main Stream filament; dense, isolated clouds which follow the entire length of the Stream; head-tail structures; and a complex filamentary web at the head where gas is being freshly stripped away from the Small Magellanic Cloud and the Bridge. Debris which appears to be of Magellanic origin extends out to 20°from the main Stream filaments. The large number of elongated Stream clouds suggests the presence of shearing motions within the Stream, arising from tidal forces or interaction with the tenuous Galactic halo. Clouds along the sightline to the less distant half of the Sculptor Group, show anomalous properties. We argue that these clouds represent halo material, and are not distant Sculptor Group clouds. This result has significant implications for the hypothesis that there might exist distant, massive HVCs within the Local Group. (abridged)

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arXiv2001

Neutral Hydrogen and the Missing Satellites of the Local Group

We present a comparison of the leftover satellites at z=0 in a cold dark matter dominated simulation of the formation of the Local Group to the distribution of observed neutral hydrogen high-velocity clouds and compact high-velocity clouds. The ~2000 leftover satellites in the simulation have dark matter masses which range between 0.5 to 10 x 10^9 Msun, sizes between 3 to 30 kpc, and distances between 100 kpc and 2 Mpc. The dark matter halos show a clear bias in their distribution towards M31 and to a lesser extent towards the Local Group anti-barycenter. If the Local Group halos contain ~1% of their dark matter mass in neutral hydrogen they should have been easily detected by the current HI surveys. The only HI objects detected with the potential to be the Local Group halos are the high-velocity clouds. Here the spatial, kinematic, and HI flux properties of the clouds and dark matter halos are compared. Several different subsets of halos which may be more likely to contain neutral hydrogen are investigated, and the HVCs are found to have some similar properties to those halos within 500 kpc of the Galaxy and those halos with dark matter masses > 2 x 10^8 Msun. The compact high-velocity clouds do not show similar properties to the halos.

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arXiv2001

HIPASS High-Velocity Clouds: Properties of the Compact and Extended Populations

A catalog of Southern anomalous-velocity HI clouds at Decl. < +2 deg is presented, based on data from the HI Parkes All-Sky Survey (HIPASS). The improved sensitivity (5sigma: T_B = 0.04 K) and resolution (15.5') of the HIPASS data results in a substantial increase in the number of individual clouds (1956, as well as 41 galaxies) compared to previous surveys. Most high-velocity emission features, HVCs, have a filamentary morphology and are loosely organized into large complexes extending over tens of degrees. In addition, 179 compact and isolated anomalous-velocity objects, CHVCs, are identified based on their size and degree of isolation. 25% of the CHVCs originally classified by Braun & Burton (1999) are reclassified. Both the entire population of high-velocity emission features and the CHVCs alone have typical HI masses of ~ 4.5 D(kpc)^2 solar masses and have similar slopes for their column density and flux distributions. On the other hand, the CHVCs appear to be clustered and the population can be broken up into three spatially distinct groups, while the entire population of clouds is more uniformly distributed with a significant percentage aligned with the Magellanic Stream. The median velocities are V_GSR = -38 km/s for the CHVCs and -30 km/s for all of the anomalous-velocity clouds. Based on the catalog sizes, high-velocity features cover 19% of the southern sky and CHVCs cover 1%. (abridged)

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arXiv2001

The Galactic Halo UV Field, Magellanic Stream and High Velocity Clouds

Significant numbers of high-velocity HI clouds (HVCs) have now been detected in H-alpha, with a subset seen in low ionization lines (e.g. [NII]). It was originally hoped that the observed H-alpha strength would provide a distance constraint to individual clouds. This idea requires that a useful fraction (f_esc > 1%) of ionizing photons escape the Galaxy, and that the halo ionizing field is relatively smooth, as we discuss. Most HVCs which are known to be close to the Sun are H-alpha; the brightest clouds also show enhanced [NII] emission, in contrast to the Magellanic Stream where the low ionization emission lines are always weak compared to H-alpha. But an acute complication for H-alpha distances is the apparent H-alpha brightness of the Magellanic Stream along several sight lines. To account for this, we present three possible configurations for the Magellanic Stream and propose a follow-up experiment. If we normalize the distances to local HVCs, some HVCs appear to be scattered throughout the Galactic halo on scales of tens of kiloparsecs.

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arXiv2001

High-Velocity Clouds Related to the Magellanic System

The results of the interaction between the Milky Way and the Magellanic Clouds are revealed through several high velocity complexes which are connected to the Clouds. The exact mechanism of their formation is under some debate, but they remain the only group of high-velocity clouds (HVCs) for which we have an origin and roughly a distance. Given that, the Magellanic HVCs can be used as a calibrator for other HVCs, while also providing an opportunity to closely investigate the remnants of an interacting system. These HVCs may hold the key to the star formation history, kinematic structure, and present Hubble type of the Magellanic Clouds, and their proximity to the Milky Way allows us to estimate key Galactic parameters. The HVCs related to the Magellanic System can be classified into three major complexes: the Magellanic Bridge, an HI connection between the Clouds; the Magellanic Stream, which trails the clouds and is one of the largest HI features in the sky outside of our Galaxy; and the Leading Arm, a more diffuse HI filament which leads the Clouds. In terms of HVCs, these features have been studied rather extensively. In this review, I will first describe the observational results for each complex and subsequently discuss their origin and relationship to the overall HVC population. All of the HI data presented are from the HI Parkes All-Sky Survey (HIPASS) (Barnes et al. 2001; Putman et al. 2001).

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arXiv2001

HI spectra and column densities toward HVC and IVC probes

We show 21-cm line profiles in the direction of stars and extragalactic objects, lying projected on high- and intermediate-velocity clouds (HVCs and IVCs). About half of these are from new data obtained with the Effelsberg 100-m telescope, about a quarter are extracted from the Leiden-Dwingeloo Survey (LDS) and the remaining quarter were observed with other single-dish telescopes. HI column densities were determined for each HVC/IVC. Wakker (2001) (Paper I) uses these in combination with optical and ultraviolet high-resolution measurements to derive abundances. Here, an analysis is given of the difference and ratio of N(HI) as observed with a 9 arcmin versus a 35 arcmin beam. For HVCs and IVCs the ratio N(HI-9 arcmin)/N(HI-35 arcmin) lies in the range 0.2-2.5. For low-velocity gas this ratio ranges from 0.75 to 1.3 (the observed ratio is 0.85-1.4, but it appears that the correction for stray radiation is slightly off). The smaller range for the low-velocity gas may be caused by confusion in the line of sight, so that a low ratio in one component can be compensated by a high ratio in another -- for 11 low-velocity clouds fit by one component the distribution of ratios has a larger dispersion. Comparison with higher angular resolution data is possible for sixteen sightlines. Eight sightlines with HI data at 1 arcmin-2 arcmin resolution show a range of 0.75-1.25 for N(HI-2 arcmin)/N(HI-9 arcmin), while in eight other sightlines N(HI-Ly-alpha)/N(HI-9 arcmin) ranges from 0.74 to 0.98.

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