arXiv subjects

Jason Tumlinson

Publications and source records attributed to Jason Tumlinson.

At least 55 records · Page 3Linked to original sources

arXiv2020

First Co-spatial Comparison of Stellar, Neutral-, and Ionized-gas Metallicities in a metal-rich galaxy: M83

We carry out a comparative analysis of the metallicities from the stellar, neutral-gas, and ionized-gas components in the metal-rich spiral galaxy M83. We analyze spectroscopic observations taken with the Hubble Space Telescope (HST), the Large Binocular Telescope (LBT) and the Very Large Telescope (VLT). We detect a clear depletion of the HI gas, as observed from the HI column densities in the nuclear region of this spiral galaxy. We find column densities of log[$N$(HI) cm$^{-2}$] $<$ 20.0 at galactocentric distances of $<$ 0.18 kpc, in contrast to column densities of log[$N$(HI) cm$^{-2}$] $\sim$ 21.0 in the galactic disk, a trend observed in other nearby spiral galaxies. We measure a metallicity gradient of $-$0.03 $\pm$ 0.01 dex kpc$^{-1}$ for the ionized gas, comparable to the metallicity gradient of a local benchmark of 49 nearby star-forming galaxies of $-$0.026 $\pm$ 0.002 dex kpc$^{-1}$. Our co-spatial metallicity comparison of the multi-phase gas and stellar populations shows excellent agreement outside of the nucleus of the galaxy hinting at a scenario where the mixing of newly synthesized metals from the most massive stars in the star clusters takes longer than their lifetimes ($\sim$10 Myr). Finally, our work shows that caution must be taken when studying the metallicity gradient of the neutral-gas component in star-forming galaxies, since this can be strongly biased, as these environments can be dominated by molecular gas. In these regions the typical metallicity tracers can provide inaccurate abundances as they may trace both the neutral- and molecular-gas components.

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arXiv2020

Figuring Out Gas & Galaxies in Enzo (FOGGIE). III. The Mocky Way: Investigating Biases in Observing the Milky Way's Circumgalactic Medium

The circumgalactic medium (CGM) of the Milky Way is mostly obscured by nearby gas in position-velocity space because we reside inside the Galaxy. Substantial biases exist in most studies on the Milky Way's CGM that focus on easier-to-detect high-velocity gas. With mock observations on a Milky-Way analog from the FOGGIE simulation, we investigate four observational biases related to the Milky Way's CGM. First, QSO absorption-line studies probe a limited amount of the CGM mass: only 35% of the mass is at high Galactic latitudes $|b|>20$ degrees, of which only half is moving at $|v_{\rm LSR}|\gtrsim100$ km s$^{-1}$. Second, the inflow rate ($\dot{M}$) of the cold gas observable in HI 21cm is reduced by a factor of $\sim10$ as we switch from the local standard of rest to the galaxy's rest frame; meanwhile $\dot{M}$ of the cool and warm gas does not change significantly. Third, OVI and NV are promising ions to probe the Milky Way's outer CGM ($r\gtrsim$15 kpc), but CIV may be less sensitive. Lastly, the scatter in ion column density is a factor of 2 higher if the CGM is observed from inside-out than from external views because of the gas radial density profile. Our work highlights that observations of the Milky Way's CGM, especially those using HI 21cm and QSO absorption lines, are highly biased. We demonstrate that these biases can be quantified and calibrated through synthetic observations with simulated Milky-Way analogs.

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arXiv2020

The Semi-forbidden CIII]$λ$1909Å~ Emission in the Rest-Ultraviolet Spectra of Green Pea Galaxies

We used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to observe the semi-forbidden CIII] emission in Green Pea galaxies at 0.13 < z < 0.3. We detect CIII] emission in 7/10 galaxies with CIII] equivalent widths that range from 2-10Å~. The observed CIII] emission line strengths are consistent with the predictions from photoionization models which incorporate the effects of binary stellar evolution with young stellar ages < 3-5 Myrs, and high ionization parameters (logU > -2). The hard ionizing radiation from young massive stars, and high nebular temperatures at low-metallicities can account for the observed high equivalent widths of CIII] and [OIII] emission lines. The Green Pea galaxies do not show a significant correlation between the Ly$α$ and CIII] equivalent widths, and the observed scatter is likely due to the variations in the optical depth of Ly$α$ to the neutral gas. Green Pea galaxies are likely to be density-bounded, and we examined the dependence of CIII] emission on the Lyman continuum optical depth. The potential LyC leaker galaxies in our sample have high CIII] equivalent widths that can only be reproduced by starburst ages as young as < 3 Myrs and harder ionizing spectra than the non-leakers. Among the galaxies with similar metallicities and ionization parameters, the CIII] equivalent width appears to be stronger for those with higher optical depth to LyC, as expected from the photoionization models. Further investigation of a larger sample of CIII]-emitters is necessary to calibrate the dependence of CIII] emission on the escape of LyC radiation, and to enable application of the CIII] diagnostics to galaxies in the reionization epoch.

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arXiv2020

Figuring Out Gas & Galaxies In Enzo (FOGGIE). IV. The Stochasticity of Ram Pressure Stripping in Galactic Halos

We study ram pressure stripping in simulated Milky Way-like halos at z>=2 from the Figuring Out Gas & Galaxies In Enzo (FOGGIE) project. These simulations reach exquisite resolution in their circumgalactic medium (CGM) gas owing to FOGGIE's novel refinement scheme. The CGM of each halo spans a wide dynamic range in density and velocity over its volume---roughly 6 dex and 1000 km/s, respectively---translating into a 5 dex range in ram pressure imparted to interacting satellites. The ram pressure profiles of the simulated CGM are highly stochastic, owing to kpc-scale variations of the density and velocity fields of the CGM gas. As a result, the efficacy of ram pressure stripping depends strongly on the specific path a satellite takes through the CGM. The ram-pressure history of a single satellite is generally unpredictable and not well correlated with its approach vector with respect to the host galaxy. The cumulative impact of ram pressure on the simulated satellites is dominated by only a few short strong impulses---on average, 90% of the total surface momentum gained through ram pressure is imparted in 20% or less of the total orbital time. These results reveal an erratic mode of ram pressure stripping in Milky-Way like halos at high redshift---one that is not captured by a smooth spherically-averaged model of the circumgalactic medium.

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arXiv2020

Newly Improved Ionization Corrections for the Neutral Interstellar Medium: Enabling Accurate Abundance Determinations in Star-forming Galaxies throughout the Universe

Studies measuring the chemical abundances of the neutral gas in star-forming galaxies (SFGs) require ionization correction factors (ICFs) to accurately measure their metal contents. In the work presented here we calculate newly improved ICFs for a sample of SFGs. These new corrections include both the contaminating ionized gas along the line of sight (ICF$_{\rm ionized}$) and unaccounted higher ionization stages in the neutral gas (ICF$_{\rm neutral}$). We make use of recently acquired spectroscopic observations taken with the Cosmic Origins Spectrograph (COS) on board Hubble to measure column densities for Fe II and Fe III. Using the Fe III/Fe II ratios as well as other physical properties (i.e. $\log$[L$_{\rm UV}$], $N$(H I), T, and $Z$) we generate ad-hoc photoionization models with CLOUDY to quantify the corrections required for each of the targets. We identify a luminosity threshold of $\log$[L$_{\rm UV}$]$\sim$ 40.75 erg s$^{-1}$ above which the ICF$_{\rm neutral}$ values for nitrogen are relatively higher (ICF$_{\rm neutral}=0.05$-0.7) than those for the rest of the elements (ICF$_{\rm neutral}\sim 0.01$). This behavior indicates that for the high UV luminosity objects, N II is found in non-negligible quantities in the neutral gas, making these ICF$_{\rm neutral}$ corrections critical for determining the true abundances in the interstellar medium. In addition, we calculate ICFs from a uniform grid of models covering a wide range of physical properties typically observed in studies of SFGs and extragalactic H II regions. We provide the community with tabulated ICF values for the neutral gas abundances measured from a variety of environments and applicable to chemical studies of the high redshift universe.

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arXiv2020

Project AMIGA: The Circumgalactic Medium of Andromeda

Project AMIGA (Absorption Maps In the Gas of Andromeda) is a large ultraviolet Hubble Space Telescope program, which has assembled a sample of 43 QSOs that pierce the circumgalactic medium (CGM) of Andromeda (M31) from R=25 to 569 kpc (25 of them probing gas from 25 kpc to about the virial radius-Rvir = 300 kpc-of M31). Our large sample provides an unparalleled look at the physical conditions and distribution of metals in the CGM of a single galaxy using ions that probe a wide range of gas phases (Si II, Si III, Si IV, C II, C IV, and O VI, the latter being from the Far Ultraviolet Spectroscopic Explorer). We find that Si III and O VI have near unity covering factor maintained all the way out to 1.2Rvir and 1.9Rvir, respectively. We show that Si III is the dominant ion over Si II and Si IV at any R. While we do not find that the properties of the CGM of M31 depend strongly on the azimuth, we show that they change remarkably around 0.3-0.5Rvir, conveying that the inner regions of the CGM of M31 are more dynamic and have more complicated multi-phase gas-structures than at R>0.5Rvir. We estimate the metal mass of the CGM within Rvir as probed by Si II, Si III, and Si IV is 2x10^7 Msun and by O VI is >8x10^7 Msun, while the baryon mass of the 10^4-10^5.5 K gas is ~4x10^10 (Z/0.3 Zsun)^(-1) Msun within Rvir. We show that different zoom-in cosmological simulations of L* galaxies better reproduce the column density profile of O VI with R than Si III or the other studied ions. We find that observations of the M31 CGM and zoom-in simulations of L* galaxies have both lower ions showing higher column density dispersion and dependence on R than higher ions, indicating that the higher ionization structures are larger and/or more broadly distributed.

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arXiv2019

The COS Absorption Survey of Baryon Harbors: The Galaxy Database and Cross-Correlation Analysis of OVI Systems

We describe the survey for galaxies in the fields surrounding 9 sightlines to far-UV bright, z~1 quasars that define the COS Absorption Survey of Baryon Harbors (CASBaH) program. The photometry and spectroscopy that comprise the dataset come from a mixture of public surveys (SDSS, DECaLS) and our dedicated efforts on private facilities (Keck, MMT, LBT). We report the redshifts and stellar masses for 5902 galaxies within ~10 comoving-Mpc (cMpc) of the sightlines with a median of z=0.28 and M_* ~ 10^(10.1) Msun. This dataset, publicly available as the CASBaH specDB, forms the basis of several recent and ongoing CASBaH analyses. Here, we perform a clustering analysis of the galaxy sample with itself (auto-correlation) and against the set of OVI absorption systems (cross-correlation) discovered in the CASBaH quasar spectra with column densities N(O^+5) >= 10^(13.5)/cm^2. For each, we describe the measured clustering signal with a power-law correlation function xi(r) = (r/r_0)^(-gamma) and find that (r_0,gamma) = (5.48 +/- 0.07 h_100^-1 Mpc, 1.33 +/- 0.04) for the auto-correlation and (6.00 +/- 1 h^-1 Mpc, 1.25 +/- 0.18) for galaxy-OVI cross-correlation. We further estimate a bias factor of b_gg = 1.3 +/- 0.1 from the galaxy-galaxy auto-correlation indicating the galaxies are hosted by halos with mass M_halo ~ 10^(12.1 +/- 0.05) Msun. Finally, we estimate an OVI-galaxy bias factor b_OVI = 1.0 +/- 0.1 from the cross-correlation which is consistent with OVI absorbers being hosted by dark matter halos with typical mass M_halo ~ 10^(11) Msun. Future works with upcoming datasets (e.g., CGM^2) will improve upon these results and will assess whether any of the detected OVI arises in the intergalactic medium.

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arXiv2019

The COS Absorption Survey of Baryon Harbors (CASBaH): Warm-hot Circumgalactic Gas Reservoirs Traced by Ne VIII Absorption

We survey the highly ionized circumgalactic media (CGM) of 29 blindly selected galaxies at 0.49 < z_(gal) < 1.44 based on high-S/N ultraviolet spectra of z > 1 QSOs and the galaxy database from the COS Absorption Survey of Baryon Harbors (CASBaH). We detect the Ne VIII doublet in nine of the galaxies, and for gas with N(Ne VIII) > 10^13.3 cm^-2 (> 10^13.5 cm^-2), we derive a Ne VIII covering fraction f_c = 75 +15/-25% (44 +22/-20%) within impact parameter (rho) < 200 kpc of M_* = 10^(9.5-11.5) Msol galaxies and f_c = 70 +16/-22% (f_c = 42 +20/-17%) within rho < 1.5 virial radii. We estimate the mass in Ne VIII-traced gas to be M_gas(Ne VIII) > 10^9.5 Msol (Z/Zsol)^-1, or 6-20% of the expected baryonic mass if the Ne VIII absorbers have solar metallicity. Ionizing Ne VII to Ne VIII requires 207 eV, and photons with this energy are scarce in the CGM. However, for the median halo mass and redshift of our sample, the virial temperature is close to the peak temperature for the Ne VIII ion, and the Ne VIII-bearing gas is plausibly collisionally ionized near this temperature. Moreover, we find that photoionized Ne VIII requires cool and low-density clouds that would be highly underpressured (by approximately two orders of magnitude) relative to the putative, ambient virialized medium, complicating scenarios where such clouds could survive. Thus, more complex (e.g., non-equilibrium) models may be required; this first statistical sample of Ne VIII absorber/galaxy systems will provide stringent constraints for future CGM studies.

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arXiv2019

Evidence for an aspherical Population III supernova explosion inferred from the hyper metal-poor star HE1327-2326

We present observational evidence that an aspherical supernova explosion could have occurred in the First stars in the early universe. Our results are based on the First determination of a Zn abundance in a Hubble Space Telescope/Cosmic Origins Spectrograph high-resolution UV spectrum of a hyper metal-poor (HMP) star, HE1327-2326, with [Fe/H](NLTE) = -5.2. We determine [Zn/Fe] = 0.80$\pm$0.25 from a UV Zn I line at 2138 detected at $3.4σ$. Yields of a 25M$_{\odot}$ aspherical supernova model with artificially modified densities exploding with E = 5x10$^{51}$ ergs best match the entire abundance pattern of HE1327-2326. Such high-entropy hypernova explosions are expected to produce bipolar outfows which could facilitate the external enrichment of small neighboring galaxies. This has already been predicted by theoretical studies of the earliest star forming minihalos. Such a scenario would have significant implications for the chemical enrichment across the early universe as HMP Carbon Enhanced Metal-Poor (CEMP) stars such as HE1327-2326 might have formed in such externally enriched environments.

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arXiv2019

The Panchromatic Circumgalactic Medium

Galaxies are surrounded by extended atmospheres, which are often called the circumgalactic medium (CGM) and are the least understood part of galactic ecosystems. The CGM serves as a reservoir of both diffuse, metal-poor gas accreted from the intergalactic medium, and metal-rich gas that is either ejected from galaxies by energetic feedback or stripped from infalling satellites. As such, the CGM is empirically multi-phased and complex in dynamics. Significant progress has been made in the past decade or so in observing the cosmic-ray/B-field, as well as various phases of the CGM. But basic questions remain to be answered. First, what are the energy, mass, and metal contents of the CGM? More specifically, how are they spatially distributed and partitioned in the different components? Moreover, how are they linked to properties of host galaxies and their global clustering and intergalactic medium environments? Lastly, what are the origin, state, and life-cycle of the CGM? This question explores the dynamics of the CGM. Here we illustrate how these questions may be addressed with multi-wavelength observations of the CGM.

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arXiv2019

Astro2020 Science White Paper: Spatially Resolved UV Nebular Diagnostics in Star-Forming Galaxies

Diagnosing the physical and chemical conditions within star-forming galaxies (SFGs) is of paramount importance to understanding key components of galaxy formation and evolution: star-formation, gas enrichment, outflows, and accretion. Well established optical emission-line diagnostics used to discern such properties (i.e., metal content, density, strength/shape of ionizing radiation) will be observationally inaccessible for the earliest galaxies, emphasizing the need for robust, reliable interstellar medium (ISM) diagnostics at ultraviolet (UV) wavelengths. Calibrating these UV diagnostics requires a comprehensive comparison of the UV and optical emission lines in nearby SFGs. Optical integral field unit (IFU) surveys have revealed the inhomogeneous nature of the ISM in SFGs, which leads to non-systematic biases in the interpretation of unresolved sources. Spatial variations are especially important to consider at UV wavelengths, where the strongest emission features originate from only the highest excitation regions of the nebula and are challenging to distinguish from competing high-ionization sources (e.g., shocks, AGN, etc.). Since surveys collecting large-scale optical integral field unit (IFU) spectroscopy are already underway, this white paper calls for an IFU or multi-object far-UV (FUV) spectroscopic instrument with high sensitivity, high spatial resolution, and large field of view (FoV). Given the impact of large-scale optical IFU surveys over the past decade, this white paper emphasizes the scientific need for a comparable foundation of spatially-resolved far-UV spectroscopy survey of nearby galaxies that will lay the foundation of diagnostics critical to the interpretation of the distant universe.

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arXiv2019

Figuring Out Gas & Galaxies in Enzo (FOGGIE). I. Resolving Simulated Circumgalactic Absorption at 2 < z < 2.5

We present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project. In contrast to most extant simulations of galaxy formation, which concentrate computational resources on galactic disks and spheroids with fluid and particle elements of fixed mass, the FOGGIE simulations focus on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies. Using the Enzo code and a new refinement scheme, FOGGIE reaches spatial resolutions of 381 comoving $h^{-1}$ pc and resolves extremely low masses ($\lesssim 1$--$100$ Msun out to 100 comoving $h^{-1}$ kpc from the central halo. At these resolutions, cloud and filament-like structures giving rise to simulated absorption are smaller, and better resolved, than the same structures simulated with standard density-dependent refinement. Most of the simulated absorption arises in identifiable and well-resolved structures with masses $\lesssim 10^4$ Msun, well below the mass resolution of typical zoom simulations. However, integrated quantities such as mass surface density and ionic covering fractions change at only the $\lesssim 30$% level as resolution is varied. This relatively small changes in projected quantities---even when the sizes and distribution of absorbing clouds change dramatically---indicate that commonly used observables provide only weak constraints on the physical structure of the underlying gas. Comparing the simulated absorption features to the KODIAQ (Keck Observatory Database of Ionized Absorption toward Quasars) survey of $z \sim2$--$3.5$ Lyman limit systems, we show that high-resolution FOGGIE runs better resolve the internal kinematic structure of detected absorption, and better match the observed distribution of absorber properties. These results indicate that CGM resolution is key in properly testing simulations of galaxy evolution with circumgalactic observations.

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arXiv2019

Understanding the circumgalactic medium is critical for understanding galaxy evolution

Galaxies evolve under the influence of gas flows between their interstellar medium and their surrounding gaseous halos known as the circumgalactic medium (CGM). The CGM is a major reservoir of galactic baryons and metals, and plays a key role in the long cycles of accretion, feedback, and recycling of gas that drive star formation. In order to fully understand the physical processes at work within galaxies, it is therefore essential to have a firm understanding of the composition, structure, kinematics, thermodynamics, and evolution of the CGM. In this white paper we outline connections between the CGM and galactic star formation histories, internal kinematics, chemical evolution, quenching, satellite evolution, dark matter halo occupation, and the reionization of the larger-scale intergalactic medium in light of the advances that will be made on these topics in the 2020s. We argue that, in the next decade, fundamental progress on all of these major issues depends critically on improved empirical characterization and theoretical understanding of the CGM. In particular, we discuss how future advances in spatially-resolved CGM observations at high spectral resolution, broader characterization of the CGM across galaxy mass and redshift, and expected breakthroughs in cosmological hydrodynamic simulations will help resolve these major problems in galaxy evolution.

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arXiv2019

Discovery of a Damped Ly-alpha System in a Low-z Galaxy Group: Possible Evidence for Gas Inflow and Nuclear Star Formation

We present a low-redshift (z=0.029) Damped Lyman-alpha (DLA) system in the spectrum of a background Quasi-Stellar Object (QSO). The DLA is associated with an interacting galaxy pair within a galaxy group. We detected weak Lyman-alpha emission centered at the absorption trough of the DLA. The emission was likely tracing the neutral HI reservoir around the galaxies in the interacting pair, which scattered the Lyman-alpha generated by star formation within those galaxies. We also found that the interacting pair is enveloped by a large HI cloud with $M(HI)=2\times 10^{10}M_{\odot}$. We discovered blueshifted 21cm HI emission, corresponding to M(HI)=$ 2\times10^{9}~M_{\odot}$, associated with J151225.15+012950.4 - one of the galaxies in the interacting pair. The blueshifted HI was tracing gas flowing into the galaxy from behind and towards us. Gas at similar blueshifted velocities was seen in the QSO sightline thus suggesting the presence of a filamentary structure of the order of 100kpc feeding the galaxy. We estimated a mass inflow rate of $2 M_{\odot}~yr^{-1}$ into the galaxy, which matches the star formation rate estimated from H-alpha emission. It is likely that the inflow of enormous amounts of gas has triggered star formation in this galaxy. The sudden acquisition of cold gas may lead to a starburst in this galaxy like those commonly seen in simulations.

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arXiv2018

Figuring Out Gas & Galaxies in Enzo (FOGGIE). II. Emission from the z=3 Circumgalactic Medium

Observing the circumgalactic medium (CGM) in emission provides 3D maps of the spatial and kinematic extent of the gas that fuels galaxies and receives their feedback. We present mock emission-line maps of highly resolved CGM gas from the FOGGIE project (Figuring Out Gas & Galaxies in Enzo) and link these maps back to physical and spatial properties of the gas. By increasing the spatial resolution alone, the total luminosity of the line emission increases by an order of magnitude. This increase arises in the abundance of dense small-scale structure resolved when the CGM gas is simulated to < 100 pc scales. Current integral field unit instruments like KCWI and MUSE should be able to detect the brightest knots and filaments of such emission, and from this to infer the bulk kinematics of the CGM gas with respect to the galaxy. We conclude that accounting for small-scale structure well below the level of instrument spatial resolution is necessary to properly interpret such observations in terms of the underlying gas structure driving observable emission.

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arXiv2018

On the CGM Fundamental Plane: The Halo Mass Dependency of Circumgalactic HI

We analyze the equivalent widths of HI Ly-$α$ ($W_{Lyα}$) absorption from the inner (R < 160 kpc) circumgalactic medium (CGM) of 85 galaxies at $z \sim 0$ with stellar masses $M*$ ranging $\rm{8 \leq log M* / M_{\odot} \leq 11.6}$. Across three orders of magnitude in stellar mass, the CGM of present-day galaxies exhibits a very high covering fraction of cool hydrogen gas ($f_C = 87\pm 4$\%) indicating that the CGM is ubiquitous in modern, isolated galaxies. When HI Ly-$α$ is detected, its equivalent width declines with increasing radius regardless of the galaxy mass, but the scatter in this trend correlates closely with $M*$. Using the radial and stellar mass correlations, we construct a planar surface describing the cool CGM of modern galaxies: $\log W^{\rm{s}}_{HI 1215} \; = \; (0.34 \pm 0.02) -( 0.0026 \pm 0.0005)\times (R) + (0.286 \pm 0.002) \times \log (M*/M_{\odot})$. The RMS scatter around this bivariate relation is $\sim$0.2 dex. We interpret the explicit correlation between $W_{Lyα}$ and $M*$ to arise from the underlying dark matter halo mass ($M_{halo}$), thereby suggesting a CGM fundamental plane between $W_{Lyα}$, $R$ and $M_{halo}$. This correlation can be used to estimate the underlying dark matter halo mass from observations of saturated HI Ly-$α$ in the CGM of a modern galaxy.

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arXiv2018

The initial mass function in the Coma Berenices dwarf galaxy from deep near-infrared HST observations

We use deep $HST$ WFC3/IR imaging to study the Initial Mass Function (IMF) of the ultra faint dwarf galaxy Coma Berenices (Com Ber). Our observations reach the lowest stellar mass ever probed in a resolved galaxy, with 50\% completeness at $\sim 0.17$ M$_{\odot}$. Unresolved background galaxies however limit our purity below $\sim 0.23$ M$_{\odot}$. If modeled with a single power law, we find that the IMF slope is $-1.45^{+0.29}_{-0.3}$ (68\% credible intervals), compared to a Milky Way value of $-2.3$. For a broken power law, we obtain a low-mass slope of $-1.18_{-0.33}^{+0.49}$, a high-mass slope of $-1.88_{-0.49}^{+0.43}$ and a break mass of $0.57_{-0.08}^{+0.12}$ M$_{\odot}$, compared to $-1.3$, $-2.3$ and 0.5 M$_{\odot}$ for a Kroupa IMF. For a log-normal IMF model we obtain values of $0.33_{-0.16}^{+0.15}$ M$_{\odot}$ for the location parameter and of $0.68_{-0.12}^{+0.17}$ for $σ$ (0.22 M$_{\odot}$ and 0.57 for the Chabrier system IMF). All three parametrizations produce similar agreement with the data. Our results agree with previous analysis of shallower optical HST data. However analysis of similar optical data of other dwarfs finds IMFs significantly more bottom-light than in the Milky Way. These results suggest two, non mutually exclusive, possibilities: that the discrepancy of the dwarf galaxies IMF with respect to the Milky Way is, at least partly, an artifact of using a single power law model, and that there is real variance in the IMF at low masses between the currently studied nearby dwarfs, with Com Ber being similar to the Milky Way, but other dwarfs differing significantly.

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arXiv2018

The COS-AGN survey: Revealing the nature of circum-galactic gas around hosts of active galactic nuclei

Active galactic nuclei (AGN) are thought to play a critical role in shaping galaxies, but their effect on the circumgalactic medium (CGM) is not well studied. We present results from the COS-AGN survey: 19 quasar sightlines that probe the CGM of 20 optically-selected AGN host galaxies with impact parameters $80 < ρ_{imp} < 300$ kpc. Absorption lines from a variety of species are measured and compared to a stellar mass and impact parameter matched sample of sightlines through non-AGN galaxies. Amongst the observed species in the COS-AGN sample (HI, CII, SiII, SiIII, CIV, SiIV, NV), only Ly$α$ shows a high covering fraction ($94^{+6}_{-23}$% for rest-frame equivalent widths EW $> 124$ mÅ) whilst many of the metal ions are not detected in individual sightlines. A sightline-by-sightline comparison between COS-AGN and the control sample yields no significant difference in EW distribution. However, stacked spectra of the COS-AGN and control samples show significant (> 3 sigma) enhancements in the EW of both Ly$α$ and SiIII at impact parameters $> 164$ kpc by a factor of $+0.45\pm0.05$ dex and $> +0.75$ dex respectively. The lack of detections of both high-ionization species near the AGN and strong kinematic offsets between the absorption systemic galaxy redshifts indicates that neither the AGN's ionization nor its outflows are the origin of these differences. Instead, we suggest the observed differences could result from either AGN hosts residing in haloes with intrinsically distinct gas properties, or that their CGM has been affected by a previous event, such as a starburst, which may also have fuelled the nuclear activity.

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