arXiv subjects

Timothy Heckman

Publications and source records attributed to Timothy Heckman.

At least 73 records · Page 4Linked to original sources

arXiv2023

The Complex X-ray Obscuration Environment in the Radio Loud Type 2 Quasar 3C 223

3C 223 is a radio loud, Type 2 quasar at $z=0.1365$ with an intriguing XMM-Newton spectrum that implicated it as a rare, Compton-thick ($N_{\rm H} \gtrsim 1.25 \times 10^{24}$ cm$^{-2}$) active galactic nucleus (AGN). We obtained contemporaneous XMM-Newton and NuSTAR spectra to fit the broad-band X-ray spectrum with the physically-motivated MYTorus and borus02 models. We confirm earlier results that the obscuring gas is patchy with both high (though not Compton-thick) levels of obscuration ($N_{\rm H} > 10^{23}$ cm$^{-2}$) and gas clouds with column densities up to an order of magnitude lower. The spectral fitting results indicate additional physical processes beyond those modeled in the spectral grids of MYTorus and borus02 impact the emergent spectrum: the Compton-scattering region may be extended beyond the putative torus; a ring of heavy Compton-thick material blocks most X-ray emission along the line of sight; or the radio jet is beamed, boosting the production of Fe K$α$ line photons in the global medium compared with what is observed along the line of sight. We revisit a recent claim that no radio loud Compton-thick AGN have yet been conclusively shown to exist, finding three reported cases of radio loud AGN with global average (but not line-of-sight) column densities that are Compton-thick. Now that it is possible to separately determine line-of-sight and global column densities, inhomogeneity in the obscuring medium has consequences for how we interpet the spectrum and classify an AGN as "Compton-thick."

astro-ph.HE↗

arXiv2023

The Low-Redshift Lyman Continuum Survey: Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape

The Mg II 2796, 2803 doublet has been suggested to be a useful indirect indicator for the escape of Ly-alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here we present the first study of Mg II probing a large dynamic range of galaxy properties, using newly obtained high signal-to-noise, moderate-resolution spectra of Mg II for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles ranging from strong emission to P-Cygni profiles, and to pure absorption. We find there is a significant trend (with a possibility of spurious correlations of ~ 2%) that galaxies detected as strong LyC Emitters (LCEs) also show larger equivalent widths of Mg II emission, and non-LCEs tend to show evidence of more scattering and absorption features in Mg II We then find Mg II strongly correlates with Ly-alpha in both equivalent width and escape fraction, regardless of whether the emission or absorption dominates the Mg II profiles. Furthermore, we present that, for galaxies categorized as Mg II emitters (MgE), one can adopt the information of Mg II, metallicity, and dust to estimate the escape fraction of LyC within a factor of 3. These findings confirm that Mg II lines can be used as a tool to select galaxies as LCEs and to serve as an indirect indicator for the escape of Ly-alpha and LyC.

astro-ph.GA↗

arXiv2022

Resolved Molecular Gas Observations of MaNGA Post-starbursts Reveal a Tumultuous Past

Post-starburst galaxies (PSBs) have recently and rapidly quenched their star-formation, thus they are an important way to understand how galaxies transition from star-forming late-types to quiescent early-types. The recent discovery of large cold gas reservoirs in PSBs calls into question the theory that galaxies must lose their gas to become quiescent. Optical Integral Field Spectroscopy (IFS) surveys have revealed two classes of PSBs: central PSBs with central quenching regions and ring PSBs with quenching in their outskirts. We analyze a sample of 13 nearby (z < 0.1) PSBs with spatially resolved optical IFS data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey and matched resolution Atacama Large (sub-)Millimeter Array (ALMA) observations of $^{12}$CO(1-0). Disturbed stellar kinematics in 7/13 of our PSBs and centrally concentrated molecular gas is consistent with a recent merger for most of our sample. In galaxies without merger evidence, alternate processes may funnel gas inwards and suppress star-formation, which may include outflows, stellar bars, and minor mergers or interactions. The star-formation efficiencies of the post-starburst regions in nearly half our galaxies are suppressed while the gas fractions are consistent with star-forming galaxies. AGN feedback may drive this stabilization, and we observe AGN-consistent emission in the centers of 5/13 galaxies. Finally, our central and ring PSBs have similar properties except the ionized and molecular gas in central PSBs is more disturbed. Overall, the molecular gas in our PSBs tends to be compact and highly disturbed, resulting in concentrated gas reservoirs unable to form stars efficiently.

astro-ph.GA↗

arXiv2022

Forming Stars in a Dual AGN Host: Molecular and Ionized Gas in the Nearby, Luminous Infrared Merger, Mrk 266

We present star formation rates based on cold and ionized gas measurements of Mrk 266 (NGC 5256), a system composed of two colliding gas-rich galaxies, each hosting an active galactic nucleus. Using $^{12}$CO (1-0) observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), we find a total H$_2$ mass in the central region of $1.1\pm0.3\times10^{10}$ $M_\odot$ which leads to a possible future star formation rate of $25\pm10 M_\odot$ yr$^{-1}$. With the Fourier Transform Spectrograph (SITELLE) on the Canada-France-Hawaii Telescope, we measure an integrated H$α$ luminosity and estimate a present-day star formation rate of $15\pm2 M_\odot$ yr$^{-1}$ in the core of the system (avoiding the two active nuclei). These results confirm that Mrk 266 is an intermediate stage merger with a relatively high recent star formation rate and enough molecular gas to sustain it for a few hundred million years. Inflowing gas associated with the merger may have triggered both the starburst episode and two AGN but the two galaxy components differ: the region around the SW nucleus appears to be more active than the NE nucleus, which seems relatively quiet. We speculate that this difference may originate in the properties of the interstellar medium in the two systems.

astro-ph.GA↗

arXiv2022

First results from the JWST Early Release Science Program Q3D: Turbulent times in the life of a $z \sim 3$ extremely red quasar revealed by NIRSpec IFU

Extremely red quasars, with bolometric luminosities exceeding $10^{47}$ erg s$^{-1}$, are a fascinating high-redshift population that is absent in the local universe. They are the best candidates for supermassive black holes accreting at rates at or above the Eddington limit, and they are associated with the most rapid and powerful outflows of ionized gas known to date. They are also hosted by massive galaxies. Here we present the first integral field unit (IFU) observations of a high-redshift quasar obtained by the Near Infrared Spectrograph (NIRSpec) on board the James Webb Space Telescope (JWST), which targeted SDSSJ165202.64+172852.3, an extremely red quasar at $z=2.94$. JWST observations reveal extended ionized gas - as traced by [OIII]$λ$5007Å- in the host galaxy of the quasar, its outflow, and the circumgalactic medium. The complex morphology and kinematics imply that the quasar resides in a very dense environment with several interacting companion galaxies within projected distances of 10-15 kpc. The high density of the environment and the large velocities of the companion galaxies suggest that this system may represent the core of a forming cluster of galaxies. The system is a good candidate for a merger of two or more dark matter halos, each with a mass of a few $10^{13}$ M$_\odot$ and traces potentially one of the densest knots at $z\sim3$.

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arXiv2022

A Multiwavelength view of IC 860: What Is in Action inside Quenching Galaxies

We present a multiwavelength study of IC 860, a nearby post-starburst galaxy at the early stage of transitioning from blue and star-forming to red and quiescent. Optical images reveal a galaxy-wide, dusty outflow originating from a compact core. We find evidence for a multiphase outflow in the molecular and neutral gas phase from the CO position-velocity diagram and NaD absorption features. We constrain the neutral mass outflow rate to be ~0.5 M$_{\odot}/$yr, and the total hydrogen mass outflow rate to be ~12 M$_{\odot}$/yr. Neither outflow component seems able to escape the galaxy. We also find evidence for a recent merger in the optical images, CO spatial distribution, and kinematics, and evidence for a buried AGN in the optical emission line ratios, mid-IR properties, and radio spectral shape. The depletion time of the molecular gas reservoir under the current star formation rate is ~7 Gyr, indicating that the galaxy could stay at the intermediate stage between the blue and red sequence for a long time. Thus the timescales for a significant decline in star formation rate ("quenching") and gas depletion are not necessarily the same. Our analysis supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling the gas and shed light on possible ongoing activities in similar quenching galaxies.

astro-ph.GA↗

arXiv2022

CLASSY V: The impact of aperture effects on the inferred nebular properties of local star-forming galaxies

Strong nebular emission lines are an important diagnostic tool for tracing the evolution of star-forming galaxies across cosmic time. However, different observational setups can affect these lines, and the derivation of the physical nebular properties. We analyze 12 local star-forming galaxies from the COS Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different aperture combinations on the determination of the physical conditions and gas-phase metallicity. We compare optical spectra observed with the SDSS aperture, which has a 3" of diameter similar to COS, to IFU and longslit spectra, including new LBT/MODS observations of five CLASSY galaxies. We calculate the reddening, electron densities and temperatures, metallicities, star formation rates, and equivalent widths (EWs). We find that measurements of the electron densities and temperatures, and metallicity remained roughly constant with aperture size, indicating that the gas conditions are relatively uniform for this sample. However, using the IFU observations of 3 galaxies, we find that the E(B-V) values derived from the Balmer ratios decrease ( by up to 53%) with increasing aperture size. The values change most significantly in the center of the galaxies, and level out near the COS aperture diameter of 2.5". We examine the relative contributions from the gas and stars using the H$α$ and [OIII] $λ$5007 EWs as a function of aperture light fraction, but find little to no variations within a given galaxy. These results imply that the optical spectra provide nebular properties appropriate for the FUV CLASSY spectra, even when narrow 1.0" long-slit observations are used.

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arXiv2022

CLASSY II: A technical Overview of the COS Legacy Archive Spectroscopic SurveY

The COS Legacy Archive Spectroscopic SurveY (CLASSY) is designed to provide the community with a spectral atlas of 45 nearby star-forming galaxies which were chosen to cover similar properties as those seen at high-z (z>6). The prime high level science product of CLASSY is accurately coadded UV spectra, ranging from ~1000-2000A, derived from a combination of archival and new data obtained with HST's Cosmic Origins Spectrograph (COS). This paper details the multi-stage technical processes of creating this prime data product, and the methodologies involved in extracting, reducing, aligning, and coadding far-ultraviolet (FUV) and near-ultraviolet (NUV) spectra. We provide guidelines on how to successfully utilize COS observations of extended sources, despite COS being optimized for point sources, and best-practice recommendations for the coaddition of UV spectra in general. Moreover, we discuss the effects of our reduction and coaddition techniques in the scientific application of the CLASSY data. In particular, we find that accurately accounting for flux calibration offsets can affect the derived properties of the stellar populations, while customized extractions of NUV spectra for extended sources are essential for correctly diagnosing the metallicity of galaxies via CIII] nebular emission. Despite changes in spectral resolution of up to ~25% between individual datasets (due to changes in the COS line spread function), no adverse affects were observed on the difference in velocity width and outflow velocities of isolated absorption lines when measured in the final combined data products, owing in-part to our signal-to-noise regime of S/N<20.

astro-ph.GA↗

arXiv2022

Tracing Lyman-alpha and Lyman Continuum Escape in Galaxies with Mg II Emission

Star-forming galaxies are considered the likeliest source of the H I ionizing Lyman Continuum (LyC) photons that reionized the intergalactic medium at high redshifts. However, above z >~ 6, the neutral intergalactic medium prevents direct observations of LyC. Therefore, recent years have seen the development of indirect indicators for LyC that can be calibrated at lower redshifts and applied in the Epoch of Reionization. Emission from Mg II \ly\ly 2796, 2803 doublet has been proposed as a promising LyC proxy. In this paper, we present new Hubble Space Telescope/Cosmic Origins Spectrograph observations for 8 LyC emitter candidates, selected to have strong Mg II emission lines. We securely detect LyC emission in 50% (4/8) galaxies with 2$σ$ significance. This high detection rate suggests that strong Mg II emitters might be more likely to leak LyC than similar galaxies without strong Mg II. Using photoionization models, we constrain the escape fraction of Mg II as ~ 15 -- 60%. We confirm that the escape fraction of Mg II correlates tightly with that of Lyman-alpha (LyA), which we interpret as an indication that the escape fraction of both species is controlled by resonant scattering in the same low column density gas. Furthermore, we show that the combination of the Mg II emission and dust attenuation can be used to estimate the escape fraction of LyC statistically. These findings confirm that Mg II emission can be adopted to estimate the escape fraction of LyA and LyC in local star-forming galaxies and may serve as a useful indirect indicator at the Epoch of Reionization.

astro-ph.GA↗

arXiv2022

CLASSY III: The Properties of Starburst-Driven Warm Ionized Outflows

We report the results of analyses of galactic outflows in a sample of 45 low-redshift starburst galaxies in the COS Legacy Archive Spectroscopic SurveY (CLASSY), augmented by five additional similar starbursts with COS data. The outflows are traced by blueshifted absorption-lines of metals spanning a wide range of ionization potential. The high quality and broad spectral coverage of CLASSY data enable us to disentangle the absorption due to the static ISM from that due to outflows. We further use different line multiplets and doublets to determine the covering fraction, column density, and ionization state as a function of velocity for each outflow. We measure the outflow's mean velocity and velocity width, and find that both correlate in a highly significant way with the star-formation rate, galaxy mass, and circular velocity over ranges of four orders-of-magnitude for the first two properties. We also estimate outflow rates of metals, mass, momentum, and kinetic energy. We find that, at most, only about 20% of silicon created and ejected by supernovae in the starburst is carried in the warm phase we observe. The outflows' mass-loading factor increases steeply and inversely with both circular and outflow velocity (log-log slope $\sim$ -1.6), and reaches $\sim 10$ for dwarf galaxies. We find that the outflows typically carry about 10 to 100% of the momentum injected by massive stars and about 1 to 20% of the kinetic energy. We show that these results place interesting constraints on, and new insights into, models and simulations of galactic winds.

astro-ph.GA↗

arXiv2022

The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics

The Lyman continuum (LyC) cannot be observed at the epoch of reionization (z {\gtrsim} 6) due to intergalactic H I absorption. To identify Lyman continuum emitters (LCEs) and infer the fraction of escaping LyC, astronomers have developed various indirect diagnostics of LyC escape. Using measurements of the LyC from the Low-redshift Lyman Continuum Survey (LzLCS), we present the first statistical test of these diagnostics. While optical depth indicators based on Lyα, such as peak velocity separation and equivalent width, perform well, we also find that other diagnostics, such as the [O III]/[O II] flux ratio and star formation rate surface density, predict whether a galaxy is a LCE. The relationship between these galaxy properties and the fraction of escaping LyC flux suggests that LyC escape depends strongly on H I column density, ionization parameter, and stellar feedback. We find LCEs occupy a range of stellar masses, metallicities, star formation histories, and ionization parameters, which may indicate episodic and/or different physical causes of LyC escape.

astro-ph.GA↗

arXiv2022

The COS Legacy Archive Spectroscopy SurveY (CLASSY) Treasury Atlas

Far-ultraviolet (FUV; ~1200-2000 angstroms) spectra are fundamental to our understanding of star-forming galaxies, providing a unique window on massive stellar populations, chemical evolution, feedback processes, and reionization. The launch of JWST will soon usher in a new era, pushing the UV spectroscopic frontier to higher redshifts than ever before, however, its success hinges on a comprehensive understanding of the massive star populations and gas conditions that power the observed UV spectral features. This requires a level of detail that is only possible with a combination of ample wavelength coverage, signal-to-noise, spectral-resolution, and sample diversity that has not yet been achieved by any FUV spectral database. We present the COS Legacy Spectroscopic SurveY (CLASSY) treasury and its first high level science product, the CLASSY atlas. CLASSY builds on the HST archive to construct the first high-quality (S/N_1500 >~ 5/resel), high-resolution (R~15,000) FUV spectral database of 45 nearby (0.002 < z < 0.182) star-forming galaxies. The CLASSY atlas, available to the public via the CLASSY website, is the result of optimally extracting and coadding 170 archival+new spectra from 312 orbits of HST observations. The CLASSY sample covers a broad range of properties including stellar mass (6.2 < logM_star(M_sol) < 10.1), star formation rate (-2.0 < log SFR (M_sol/yr) < +1.6), direct gas-phase metallicity (7.0 < 12+log(O/H) < 8.8), ionization (0.5 < O_32 < 38.0), reddening (0.02 < E(B-V < 0.67), and nebular density (10 < n_e (cm^-3) < 1120). CLASSY is biased to UV-bright star-forming galaxies, resulting in a sample that is consistent with z~0 mass-metallicity relationship, but is offset to higher SFRs by roughly 2 dex, similar to z >~2 galaxies. This unique set of properties makes the CLASSY atlas the benchmark training set for star-forming galaxies across cosmic time.

astro-ph.GA↗

arXiv2022

The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters

The origins of Lyman continuum (LyC) photons responsible for the reionization of the universe are as of yet unknown and highly contested. Detecting LyC photons from the epoch of reionization is not possible due to absorption by the intergalactic medium, which has prompted the development of several indirect diagnostics to infer the rate at which galaxies contribute LyC photons to reionize the universe by studying lower-redshift analogs. We present the Low-redshift Lyman Continuum Survey (LzLCS) comprising measurements made with HST/COS for a z=0.2-0.4 sample of 66 galaxies. After careful processing of the FUV spectra, we obtain a total of 35 Lyman continuum emitters (LCEs) detected with 97.725% confidence, nearly tripling the number of known local LCEs. We estimate escape fractions from the detected LyC flux and upper limits on the undetected LyC flux, finding a range of LyC escape fractions up to 50%. Of the 35 LzLCS LCEs, 12 have LyC escape fractions greater than 5%, more than doubling the number of known local LCEs with cosmologically relevant LyC escape.

astro-ph.GA↗

arXiv2021

DIISC-II: Unveiling the Connections between Star Formation and ISM in the Extended Ultraviolet Disk of NGC 3344

We present our investigation of the Extended Ultraviolet (XUV) disk galaxy, NGC 3344, conducted as part of Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey. We use surface and aperture photometry of individual young stellar complexes to study star formation and its effect on the physical properties of the interstellar medium. We measure the specific star-formation rate (sSFR) and find it to increase from $\rm10^{-10} yr^{-1}$ in the inner disk to $\rm>10^{-8} yr^{-1}$ in the extended disk. This provides evidence for inside-out disk growth. If these sSFRs are maintained, the XUV disk stellar mass can double in $\sim$0.5 Gyr, suggesting a burst of star formation. The XUV disk will continue forming stars for a long time due to the high gas depletion times ($τ_{dep}$). The stellar complexes in the XUV disk have high-$Σ_{HI}$ and low-$Σ_{SFR}$ with $τ_{dep}\sim$10 Gyrs, marking the onset of a deviation from the traditional Kennicutt-Schmidt law. We find that both far-ultraviolet (FUV) and a combination of FUV and 24$μ$m effectively trace star formation in the XUV disk. H$α$ is weaker in general and prone to stochasticities in the formation of massive stars. Investigation of the circumgalactic medium at 29.5 kpc resulted in the detection of two absorbing systems with metal-line species: the stronger absorption component is consistent with gas flows around the disk, most likely tracing inflow, while the weaker component is likely tracing corotating circumgalactic gas.

astro-ph.GA↗

arXiv2021

Detection of a Multiphase Intragroup Medium: Results from the COS-IGrM Survey

We present the results of the COS Intragroup Medium (COS-IGrM) Survey that used the Cosmic Origins Spectrograph on the Hubble Space Telescope to observe a sample of 18 UV bright quasars, each probing the intragroup medium (IGrM) of a galaxy group. We detect Ly$α$, C II, N V, Si II, Si III, and O VI in multiple sightlines. The highest ionization species detected in our data is O VI, which was detected in 8 out of 18 quasar sightlines. The wide range of ionization states observed provide evidence that the IGrM is patchy and multiphase. We find that the O VI detections generally align with radiatively cooling gas between $10^{5.8}$ and $10^6$ K. The lack of O VI detections in 10 of the 18 groups illustrates that O VI may not be the ideal tracer of the volume filling component of the IGrM. Instead, it either exists at trace levels in a hot IGrM or is generated in the boundary between the hotter IGrM and cooler gas.

astro-ph.GA↗

arXiv2021

Lower-Luminosity Obscured AGN Host Galaxies are Not Predominantly in Major-Merging Systems at Cosmic Noon

For over 60 years, the scientific community has studied actively growing central super-massive black holes (active galactic nuclei -- AGN) but fundamental questions on their genesis remain unanswered. Numerical simulations and theoretical arguments show that black hole growth occurs during short-lived periods ($\sim$ 10$^{7}$ -10$^{8}$ yr) of powerful accretion. Major mergers are commonly invoked as the most likely dissipative process to trigger the rapid fueling of AGN. If the AGN-merger paradigm is true, we expect galaxy mergers to coincide with black hole accretion during a heavily obscured AGN phase (N$_H$ $ > 10^{23}$ cm$^{-2}$). Starting from one of the largest samples of obscured AGN at 0.5 $<$ $z$ $<$ 3.1, we select 40 non-starbursting lower-luminosity obscured AGN. We then construct a one-to-one matched redshift- and near-IR magnitude-matched non-starbursting inactive galaxy control sample. Combining deep color \textit{Hubble Space Telescope} imaging and a novel method of human classification, we test the merger-AGN paradigm prediction that heavily obscured AGN are strongly associated with galaxies undergoing a major merger. On the total sample of 80 galaxies, we estimate each individual classifier's accuracy at identifying merging galaxies/post-merging systems and isolated galaxies. We calculate the probability of each galaxy being in either a major merger or isolated system, given the accuracy of the human classifiers and the individual classifications of each galaxy. We do not find statistically significant evidence that obscured AGN at cosmic noon are predominately found in systems with evidence of significant merging/post-merging features.

astro-ph.GA↗

arXiv2021

Merger or Not: Accounting for Human Biases in Identifying Galactic Merger Signatures

Significant galaxy mergers throughout cosmic time play a fundamental role in theories of galaxy evolution. The widespread usage of human classifiers to visually assess whether galaxies are in merging systems remains a fundamental component of many morphology studies. Studies that employ human classifiers usually construct a control sample, and rely on the assumption that the bias introduced by using humans will be evenly applied to all samples. In this work, we test this assumption and develop methods to correct for it. Using the standard binomial statistical methods employed in many morphology studies, we find that the merger fraction, error, and the significance of the difference between two samples are dependent on the intrinsic merger fraction of any given sample. We propose a method of quantifying merger biases of individual human classifiers and incorporate these biases into a full probabilistic model to determine the merger fraction and the probability of an individual galaxy being in a merger. Using 14 simulated human responses and accuracies, we are able to correctly label a galaxy as ''merger'' or ''isolated'' to within 1\% of the truth. Using 14 real human responses on a set of realistic mock galaxy simulation snapshots our model is able to recover the pre-coalesced merger fraction to within 10\%. Our method can not only increase the accuracy of studies probing the merger state of galaxies at cosmic noon, but also can be used to construct more accurate training sets in machine learning studies that use human classified data-sets.

astro-ph.GA↗

arXiv2020

Evidence for the Accretion of Gas in Star-Forming Galaxies: High N/O Abundances in Regions of Anomalously-Low Metallicity

While all models for the evolution of galaxies require the accretion of gas to sustain their growth via on-going star formation, it has proven difficult to directly detect this inflowing material. In this paper we use data of nearby star-forming galaxies in the SDSS IV Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to search for evidence of accretion imprinted in the chemical composition of the interstellar medium. We measure both the O/H and N/O abundance ratios in regions previously identified as having anomalously low values of O/H. We show that the unusual locations of these regions in the N/O vs. O/H plane indicate that they have been created through the mixing of disk gas having higher metallicity with accreted gas having lower metallicity. Taken together with previous analysis on these anomalously low-metallicity regions, these results imply that accretion of metal-poor gas can probably sustain star formation in present-day late-type galaxies.

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