Dwarf Starburst Galaxy Research Articles

Discovery of a 3.6 hr Eclipsing Luminous X‐Ray Binary in the Galaxy NGC 4214

We report the discovery of an eclipsing X-ray binary with a 3.62-hr period within 24 of the center of the dwarf starburst galaxy NGC 4214. The orbital period places interesting constraints on the nature of the binary, and allows for a few very different interpretations. The most likely possibility is that the source lies within NGC 4214 and has an X-ray luminosity of up to 7 e38 ergs/s. In this case the binary may well be comprised of a naked He-burning donor star with a neutron-star accretor, though a stellar-mass black-hole accretor cannot be completely excluded. There is no obvious evidence for a strong stellar wind in the X-ray orbital light curve that would be expected from a massive He star; thus, the mass of the He star should be <3-4 solar masses. If correct, this would represent a new class of very luminous X-ray binary -- perhaps related to Cyg X-3. Other less likely possibilities include a conventional low-mass X-ray binary that somehow manages to produce such a high X-ray luminosity and is apparently persistent over an interval of years; or a foreground AM Her binary of much lower luminosity that fortuitously lies in the direction of NGC 4214. Any model for this system must accommodate the lack of an optical counterpart down to a limiting magnitude of 22.6 in the visible.

First detection of Lyman continuum escape from a local starburst galaxy

Context: The dominating reionization source in the young universe has not yet been identified. Possible candidates include metal poor dwarf galaxies with starburst properties.Aims. We selected an extreme starburst dwarf, the Blue Compact Galaxy Haro 11, with the aim of determining the Lyman continuum escape fraction from UV spectroscopy.Methods. Spectra of Haro 11 were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE). A weak signal shortwards of the Lyman break is identified as Lyman continuum (LyC) emission escaping from the ongoing starburst. From profile fitting to weak metal lines we derive column densities of the low ionization species. Adopting a metallicity typical of the H II regions of Haro 11, these data correspond to a hydrogen column density of ~10^19cm^-2. This relatively high value indicates that most of the LyC photons escape through transparent holes in the interstellar medium. We then use spectral evolutionary models to constrain the escape fraction of the produced LyC photons.Results. Assuming a normal Salpeter initial mass function we obtain a Lyman continuum escape fraction of f_esc˜ 4-10%. We argue that in a hierarchical galaxy formation scenario, the upper limit we derive for the escape rate allows for a substantial contribution to cosmic reionization by starburst dwarf galaxies at high redshifts.

Discovery of a Metal?Line Absorber Associated with a Local Dwarf Starburst Galaxy

We present optical and near-infrared images, H I 21 cm emission maps, optical spectroscopy, and Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet spectroscopy of the QSO/galaxy pair SBS 1122+594/IC 691. The QSO sight line lies at a position angle of 27 degrees from the minor axis of the nearby dwarf starburst galaxy IC 691 (cz_gal = 1204+-3 km/s, L_B ~ 0.09 L*, current star formation rate = 0.08-0.24 solar masses per year) and 33 kpc (6.6 arcmin) from its nucleus. We find that IC 691 has an H I mass of M_HI = (3.6+-0.1) x 10^8 solar masses and a dynamical mass of M_dyn = (3.1+-0.5) x 10^10 solar masses. The UV spectrum of SBS 1122+594 shows a metal-line (Ly-alpha + C IV) absorber near the redshift of IC 691 at cz_abs = 1110+-30 km/s. Since IC 691 is a dwarf starburst and the SBS 1122+594 sight line lies in the expected location for an outflowing wind, we propose that the best model for producing this metal-line absorber is a starburst wind from IC 691. We place consistent metallicity limits on IC 691 ([Z/Zsun] ~ -0.7) and the metal-line absorber ([Z/Zsun] < -0.3). We also find that the galaxy's escape velocity at the absorber location is v_esc = 80+-10 km/s and derive a wind velocity of v_w = 160+-50 km/s. Thus, the evidence suggests that IC 691 produces an unbound starburst wind that escapes from its gravitational potential to transport metals and energy to the surrounding intergalactic medium.

Subarcsecond radio observations of the dwarf starburst galaxy NGC 3077

We present the first subarcsecond radio observations of the nearby dwarf starburst galaxy NGC 3077 obtained with the MERLIN interferometer. We have detected two resolved sources which are coincident with the positions of two discrete X-ray sources detected by Chandra. One of the radio sources is associated with a supernova remnant (SNR) and the observed radio flux is consistent with having a non-thermal origin. The age of the SNRs of about 760 yr is between the average age of the SNRs detected in M82 and those detected in the Milky Way and the Large Magellanic Cloud. We use this detection to calculate a star formation rate ‐ ‐

Formation and evolution of late-type dwarf galaxies -- I. NGC 1705 and NGC 1569

(Abridged.) We present one-zone chemical evolution models for two dwarf starburst galaxies, NGC 1705 and NGC 1569. Using information about the past star formation history and initial mass function of the systems previously obtained from Hubble Space Telescope colour-magnitude diagrams, we identify possible scenarios of chemical enrichment and development of galactic winds. In order not to overestimate the current metallicity of the interstellar gas inferred from H II region spectroscopy, we suggest that the winds efficiently remove from the galaxies the metal-rich ejecta of dying stars. Conversely, requiring the final mass of neutral gas to match the value inferred from 21-cm observations implies a relatively low efficiency of interstellar medium entrainment in the outflow, thus confirming previous findings that the winds driving the evolution of typical starbursts are differential. These conclusions could be different only if the galaxies accrete huge fractions of unprocessed gas at late times. By assuming standard stellar yields we obtain a good fit to the observed nitrogen to oxygen ratio of NGC 1569, while the mean N/O ratio in NGC 1705 is overestimated by the models. Reducing the extent of hot bottom burning in low-metallicity intermediate-mass stars does not suffice to solve the problem. Localized self-pollution from stars more massive than 60 MSun in NGC 1705 and/or funneling of larger fractions of nitrogen through its winds are then left to explain the discrepancy between model predictions and observations. Inspection of the log(N/O) vs. log(O/H)+12 diagram for a sample of dwarf irregular and blue compact dwarf galaxies in the literature favours the latter hypothesis.

A model for the infrared dust emission from forming galaxies

Dust plays various important roles in galaxy formation and evolution. In the early epoch of galaxy evolution, dust is only supplied by supernovae (SNe). With the aid of a new physical model of dust production by SNe developed by Nozawa et al. (N03), we constructed a model of dust emission from forming galaxies on the basis of the theoretical framework of Takeuchi et al. (T03). N03 showed that the produced dust species depends strongly on the mixing within SNe. We treated both unmixed and mixed cases and calculated the infrared (IR) spectral energy distribution (SED) of forming galaxies for both cases. Our model SED is less luminous than the SED of T03 model by a factor of 2–3. The difference is due to our improved treatment of the ultraviolet (UV) photon absorption cross-section, as well as the different grain size and species newly adopted in this work. The SED for the unmixed case is found to have an enhanced near to mid-IR (N-MIR) continuum radiation in its early phase of the evolution (age ≲ 107.25 yr) compared with that for the mixed case. The strong N-MIR continuum is due to the emission from silicon grains, which only exist in the species of the unmixed dust production. We also calculated the IR extinction curves for forming galaxies. N03 dust was found to yield a smaller extinction than that of T03 model. For the unmixed case, near-IR (NIR) extinction is dominated by large grains of silicon and amorphous carbon, and silicate features are less prominent compared to the curve given by T03. To the contrary, the extinction curve of the mixed case has a similar shape to that of T03. Then we calculated the SED of a local starbursting dwarf galaxy SBS 0335−052. Our present model SED naturally reproduced the strong N-MIR continuum and the lack of cold far-IR emission of SBS 0335−052. We found that only the SED of unmixed case can reproduce the NIR continuum of this galaxy. We then made a prediction for the SED of another typical star-forming dwarf, I Zw 18. The MIR continuum of I Zw 18 is expected to be much weaker than that of T03 SED. We also presented the evolution of the SED of Lyman-break galaxies. Finally, we discussed the possibility of observing forming galaxies at z≳ 5.

Triggering and Feedback: The Relation between the HiGas and the Starburst in the Dwarf Galaxy NGC 1569

As part of our study on the impact of violent star formation on the interstellar medium (ISM) of dwarf galaxies, we report observations of neutral atomic hydrogen (H I) in the starburst dwarf galaxy NGC 1569. High-resolution measurements with the Very Large Array (B, C, and D configuration) are aimed at identifying morphological and kinematical signatures in H I caused by the starburst. Our kinematical data suggest a huge hole in the H I distribution, probably due to the large number of supernovae explosions in the center of the galaxy over the past 20 Myr. Investigating the large-scale H I structure, we confirm the existence of a possible H I companion and a so-called H I bridge east of NGC 1569. Furthermore, we report the detection of additional low-intensity H I halo emission, which leads us to suggest a revised halo structure. On the basis of our new picture, we discuss the origin of the halo gas and possible implications for the evolution of the starburst in NGC 1569.

AChandraX‐Ray Investigation of the Violent Interstellar Medium: From Dwarf Starbursts to Ultraluminous Infrared Galaxies

We have analyzed observations with the Chandra X-ray Observatory of the diffuse emission by hot gas in 7 dwarf starburst galaxies, 6 edge-on starburst galaxies, and 9 Ultra Luminous Infrared Galaxies. These systems cover ranges of \~ 10^4 in X-ray luminosity and several thousand in star formation rate and K-band luminosity (a proxy for stellar mass). Despite this range in fundamental parameters, we find that the properties of the diffuse X-ray emission are very similar in all three classes of starburst galaxies. The spectrum of the diffuse emission is well fit by thermal emission from gas with kT ~ 0.25 to 0.8 keV and with several-times-solar abundance ratios of alpha elements to Fe. The ratio of the thermal X-ray to far-infrared luminosity is roughly constant, as is the characteristic surface brightness of the diffuse X-ray emission. The size of the diffuse X-ray source increases systematically with both far-infrared and K-Band luminosity. All three classes show strong morphological relationships between the regions of hot gas probed by the diffuse X-ray emission and the warm gas probed by optical line emission. These findings suggest that the same physical mechanism is producing the diffuse X-ray emission in the three types of starbursts, and are consistent with that mechanism being shocks driven by a galactic superwind'' powered by the kinetic energy collectively supplied by stellar winds and supernovae in the starburst.

AChandraX-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).

AChandraX-ray survey of nearby dwarf starburst galaxies - II. Starburst properties and outflows

We present a comprehensive comparison of the X-ray properties of a sample of eight dwarf starburst galaxies observed with Chandra (IZw18, VIIZw403, NGC1569, NGC3077, NGC4214, NGC4449, NGC5253, He2–10). In PaperI 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 H ii 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 α = 0.24 ± 0.06, shallower than that of more massive starburst galaxies (α = 0.4 − 0.8) and of non-starburst galaxies (α ∼ 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 H i distribution with volume densities of 0.02 −0.06cm 3 , pressures of 1 −3 ×10 5 Kcm 3 , thermal energies of 2 − 30 × 10 54 erg, and hot gas masses of 2 − 20 × 10 6 M⊙ (∼ 1 per cent of the H i masses. On global scales, the distribution of the X-ray emission looks remarkably similar to that seen in Hα (comparing azimuthal averages); locally however their distribution is clearly distinct in many cases – this can be explained by the different emission mechanisms (forward vs. reverse shocks). Mass-loading of order 1 to 5 is required to explain the differences between the amount of hot gas and and the modelled mass-loss from massive stars. The metallicity of the dwarf galaxies correlates with the diffuse X-ray luminosity and anti-correlates with the cooling time of the hot gas. The diffuse X-ray luminosity is also a function of the current star formation rate. 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 H i envelopes such as tidal tails, however, may delay outflows on timescales exceeding those of the cooling time of the hot gas.

Faint blue galaxies revisited

If dwarf-elliptical galaxies formed their stars very rapdily (on timescales of less than 1 Gyr), they may in principle be detectable out to high redshift. Prior to the discovery of cosmic acceleration, it appeared that rapid and late formation dwarf elliptical galaxies might be required to explain the number counts of faint galaxies. A plausible hypothesis emerged: that photoionization by the UV background prevents gas cooling in low-mass halos until $z \lesssim 1.5$ . The discovery of cosmic acceleration eased the tension between predicted galaxy number counts and galaxy-evolution models. Nevertheless, there is some evidence for relatively late star formation in nearby dE's, and the photoionization delay mechanism still appears to have some merit. It is thus of interest to look back in time to see if we can find starbursting dwarf galaxies at moderate redshift. We review the connection between faint-blue galaxies and bursting-dwarf galaxies and discuss some attempts to identify progenitors to dE galaxies in the Hubble Ultra Deep Field (HUDF) observations. We find roughly 85 galaxies in the HUDF with redshifts $0.6 that appear to have formed most of their stars at $z . Of these, 70% have half-light radii less than 1.5 kpc. These are thus “smoking gun” candidates for dwarf galaxies that are either collapsing for the first time at moderate redshifts or have otherwise been unable to form stars for more than 1/3$ of a Hubble time.

Young Star Clusters: Metallicity Tracers in External Galaxies

AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent star bursts. These newly-formed clusters are built from recycled gas, pre-enriched to various levels within the interacting galaxies. Hence, star clusters of different ages represent a fossil record of the chemical enrichment history of their host galaxy, as well as of the host galaxy’s violent star formation history. We present a new set of evolutionary synthesis models of our GALEV code, specifically developed to include the gaseous emission of presently forming star clusters, and a new tool to analyze multi-color observations with our models. First results for newly-born clusters in the dwarf star-burst galaxy NGC 1569 are presented.

Young Star Clusters: Progenitors of Globular Clusters!?

AbstractStar cluster formation is a major mode of star formation in the extreme conditions of interacting galaxies and violent starbursts. Young clusters are observed to form in a variety of such galaxies, a substantial number resembling the progenitors of globular clusters in mass and size, but with significantly enhanced metallicity. From studies of the metal-poor and metal-rich star cluster populations of galaxies, we can therefore learn about the violent star formation history of these galaxies, and eventually about galaxy formation and evolution. We present a new set of evolutionary synthesis models of our GALEV code, with special emphasis on the gaseous emission of presently forming star clusters, and a new tool to compare extensive model grids with multi-color broad-band observations to determine individual cluster masses, metallicities, ages and extinction values independently. First results for young star clusters in the dwarf starburst galaxy NGC 1569 are presented. The mass distributions determined for the young clusters give valuable input to dynamical star cluster system evolution models, regarding survival and destruction of clusters. We plan to investigate an age sequence of galaxy mergers to see dynamical destruction effects in process.

Probing the Multiphase Interstellar Medium of the Dwarf Starburst Galaxy NGC 625 withFar Ultraviolet Spectroscopic ExplorerSpectroscopy

We present new FUSE spectroscopy of the dwarf starburst galaxy NGC 625. These observations probe multiple phases of the interstellar medium, including the coronal, ionized, neutral and molecular gas. This nearby (D = 3.9 +/- 0.2 Mpc) system shows a clear detection of outflowing coronal gas as traced by OVI 1032 Angstrom absorption. The centroid of the OVI profile is blueshifted with respect to the galaxy systemic velocity by ~ 30 km/sec, suggesting a low-velocity outflow. The implied OVI velocity extent is found to be 100 +/- 20 km/sec, which is fully consistent with the detected HI outflow velocity found in radio synthesis observations. We detect multiple lines of diffuse H2 absorption from the ISM of NGC 625; this is one of only a few extragalactic systems with FUSE detections of H2 lines in the Lyman and Werner bands. We find a potential abundance offset between the neutral and nebular gas that exceeds the errors on the derived column densities. Since such an offset has been found in multiple dwarf galaxies, we discuss the implications of a lower-metallicity halo surrounding the central star forming regions of dwarf galaxies. The apparent offset may be due to saturation of the observed OI line, and higher S/N observations are required to resolve this issue.

Erratum: “The Influence of Supershells and Galactic Outflows on the Escape of Ionizing Radiation from Dwarf Starburst Galaxies” (ApJ, 599, 50 [2003

Fig. 10.—Changes in the instantaneous escape fractions fesc(t) when the effect of shells of swept-up ISM is included. The model is a disk with Md 1⁄4 10 M at z 1⁄4 0, with f 1⁄4 0:06, and the Lyman continuum photon luminosities are based on the instantaneous-burst model (diamonds and solid line) with Lmech 1⁄4 10 ergs s 1 and the multiple burst model (triangles and dashed line) with Lmech 1⁄4 10 ergs s . The instantaneous escape fraction fesc(t) with shells cooled to the density expected for isothermal shocks are shown with open symbols, fesc(t) with unresolved shells in our lower resolution simulations are shown with filled symbols, and fesc(t) without shells are shown with lines. The decrease in fesc(t) is significant once the maximum effect of fully cooled shells is included, before the bubble blows out of the disk at t 8 Myr.

TheChandraview of NGC 1800 and the X-ray scaling properties of dwarf starbursts

The superb spatial resolution of Chandra is utilized to study the X-ray morphology of the dwarf starburst galaxy NGC1800 embedded in a small group of galaxies. Diffuse galactic emission is detected, extending several kpc above the galactic plane, with an overall morphology similar to the galactic winds seen in nearby X-ray bright starburst galaxies. This makes NGC1800 the most distant dwarf starburst with a clear detection of diffuse X-ray emission. The diffuse X-ray luminosity of 1.3+/-0.3 *10^38 erg/s accounts for at least 60 per cent of the total soft X-ray output of the galaxy. A hot gas temperature of kT=0.25 keV and metallicity Z~0.05Z_Sun are derived, the latter in consistency with results from optical spectroscopy of the interstellar medium. Our failure to detect any hot gas associated with the embedding galaxy group translates into an upper limit to the group X-ray luminosity of L_X<10^41 erg/s. There is no convincing evidence that the outflowing wind of NGC1800 is currently interacting with any intragroup gas, and mechanical considerations indicate that the wind can escape the galaxy and its surrounding HI halo, eventually delivering energy and metals to the intragroup gas. Properties of NGC1800 are compared to those of other dwarf starburst galaxies, and a first detailed discussion of the X-ray scaling properties of this population of objects is given, set against the equivalent results obtained for normal starburst galaxies. Results indicate that dwarf starbursts to a large degree behave as down-scaled versions of normal starburst galaxies.

Massive star-formation rates ofγ-ray burst host galaxies: An unobscured view in X-rays

The hard X-ray (2-10keV) luminosity of a star-forming galaxy tracks its population of high mass X-ray binaries and is essentially unobscured. It is therefore a practically unbiased measure of star-formation in the host galaxies of gamma-ray bursts (GRBs). Using recent and archival observations of GRBs with the XMM-Newton and Chandra X-ray observatories, limits are placed on the underlying X-ray emission from GRB hosts. Useful limits on the current massive star-formation rates (SFRs), unaffected by obscuration, are obtained for the hosts of three low redshift GRBs: GRB980425, GRB030329 and GRB031203. These limits show that though the specific SFRs may be high (as in dwarf starburst galaxies), none have massive obscured star-formation at the levels implied by the sub-mm detection of some GRB hosts. It is also shown that in cases where the faint luminosities of the late time afterglow or supernova emission are of interest, the contribution of the host galaxy to the X-ray flux may be significant.

Cosmological Feedback from High‐Redshift Dwarf Galaxies

We model how repeated supernova explosions in high-redshift dwarf starburst galaxies drive superbubbles and winds out of the galaxies. We compute the efficiencies of metal and mass ejection and energy transport from the galactic potentials, including the effect of cosmological infall of external gas. The starburst bubbles quickly blow out of small, high-redshift, galactic disks, but must compete with the ram pressure of the infalling gas to escape into intergalactic space. We show that the assumed efficiency of the star formation rate dominates the bubble evolution and the metal, mass, and energy feedback efficiencies. With star formation efficiency f*=0.01, the ram pressure of infall can confine the bubbles around high-redshift dwarf galaxies with circular velocities v_c>52 km/s. We can expect high metal and mass ejection efficiencies, and moderate energy transport efficiencies in halos with v_c~30-50 km/s and f*~0.01 as well as in halos with v_c~100 km/s and f*>>0.01. Such haloes collapse successively from 1-2 sigma peaks in LambdaCDM Gaussian density perturbations as time progresses. These dwarf galaxies can probably enrich low and high-density regions of intergalactic space with metals to 10^-3-10^-2 Zsun as they collapse at z~8 and z<5 respectively. They also may be able to provide adequate turbulent energy to prevent the collapse of other nearby halos, as well as to significantly broaden Lyman-alpha absorption lines to v_rms~20-40 km/s. We compute the timescales for the next starbursts if gas freely falls back after a starburst, and find that, for star formation efficiencies as low as f*<0.01, the next starburst should occur in less than half the Hubble time at the collapse redshift. This suggests that episodic star formation may be ubiquitous in dwarf galaxies.

The Nature of Radio Continuum Emission in the Dwarf Starburst Galaxy NGC 625

We present new multifrequency radio continuum imaging of the dwarf starburst galaxy NGC 625 obtained with the Very Large Array. Data at 20, 6, and 3.6 cm reveal global continuum emission dominated by free-free emission, with only mild synchrotron components. Each of the major H II regions is detected; the individual spectral indices are thermal for the youngest regions (showing largest Hα emission) and nonthermal for the oldest. We do not detect any sources that appear to be associated with deeply embedded, dense, young clusters, although we have discovered one low-luminosity, obscured source that has no luminous optical counterpart and resides in the region of highest optical extinction. Since NGC 625 is a Wolf-Rayet galaxy with strong recent star formation, these radio properties suggest that the youngest star formation complexes have not yet evolved to the point where their thermal spectra are significantly contaminated by synchrotron emission. The nonthermal components are associated with regions of older star formation that have smaller ionized gas components. These results imply a range of ages for the H II regions and radio components that agrees with our previous resolved stellar population analysis, where an extended burst of star formation has pervaded the disk of NGC 625 over the last ~50 Myr. We compare the nature of radio continuum emission in selected nearby dwarf starburst and Wolf-Rayet galaxies, demonstrating that thermal radio continuum emission appears to be more common in these systems than in typical H II galaxies with less recent star formation and more evolved stellar clusters.

A Keck/HIRES Study of Kinematics of the Cold Interstellar Medium in Dwarf Starburst Galaxies

We have obtained high-resolution Echelle spectra (R = 30,000-50,000) of the Na D absorption doublet (λλ5890, 5896) for six dwarf starburst galaxies and two more luminous starbursts: M82 and NGC 1614. The absorption features were separated into multiple components and separated into stellar and interstellar parts on the basis of kinematics. We find that three of the dwarfs show outflows, with an average blueshift of 27 km s-1. This is small compared with the highest velocity components in NGC 1614 and M82 (blueshifted by 150 and 91 km s-1, respectively); these two brighter galaxies also show more complex absorption profiles than the dwarfs. None of the outflow speeds clearly exceed the escape velocity of the host galaxy. Sight lines in NGC 2363 and NGC 4214 apparently intersect expanding shells. We compare the shocked gas velocity (vNa D) with the ionized gas velocity (vHα) and interpret the velocity difference as either a trapped ionization front (NGC 4214) or a leaky H II region (NGC 2363). The dwarfs show NNa D = 1011.8-1013.7cm-2, while the Na D columns in M82 and NGC 1614 are 1013.7 and 1014.0 cm-2, respectively. The mass of expelled gas is highly sensitive to outflow geometry, dust depletion, and ionization fraction, but with a simple shell model we estimate neutral outflow gas masses from ~106 to ~1010 M☉.