The Origin of Faint Tidal Features Around Galaxies in the RESOLVE Survey

We present a study of faint tidal features around galaxies in the REsolved Spectroscopy of a Local VolumE (RESOLVE) survey. Our main sample consists of 1027 galaxies of the RESOLVE survey that overlap with r-band images from the DECam Legacy Survey (DECaLS) which reach a surface brightness limit of 27.9 mag arcsec[-2] for a 3σ detection of a 100 arcsec[2] feature. The images of each galaxy were masked, smoothed, and visually inspected for signs of tidal features such as streams or shells. We find that around 21[±2]% of the galaxies inspected in the DECaLS images demonstrate this faint substructure with data of this depth, setting a lower limit on the frequency of such features in this sample. We examine the relationship between the presence of tidal features, galaxy characteristics, and environment with several metrics including atomic-gas-to-stellar mass ratio, star-formation history, morphology, distance to nearest neighboring galaxy, and group mass. We find that galaxies with tidal features tend to be gas-rich (G/S > 0.1) and that the tidal features around gas-poor and gas-rich galaxies may have different origins reflected in different trends with star formation, morphology and local environment. We observe that gas-poor galaxies with tidal features have higher stellar masses, closer distances to their nearest neighbors (for neighbors in the same group), and reside in groups with fewer members at a fixed group halo mass when compared to the rest of the gas-poor sample, suggesting the gas-poor galaxies with tidal features may contain a high fraction of galaxies currently interacting or merger remnants. Gas-rich galaxies with tidal features also are closer to their nearest neighbors (for neighbors in the same group) than those without, but also show less bulged morphologies and elevated star formation, suggesting a mixture of tidal features from current interactions, gas accretion, or accretion of small companions below the survey limit.Bachelor of Scienc

Detecting Water In the atmosphere of HR 8799 c with L-band High Dispersion Spectroscopy Aided By Adaptive Optics

High dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring spin rate. Here, we present $L$ band observations of HR 8799 c using Keck NIRSPEC (R=15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H$_2$O and CH$_4$) in the atmosphere of HR 8799 c with a template matching method, which involves cross correlation between reduced spectrum and a template spectrum. We detect H$_2$O but not CH$_4$, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high dispersion spectroscopy observations. We conclude that $10^{-4}$ contrast can be reached in $L$ band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade.Comment: 14 pages, 5 figures, 5 tables, accepted for publication on AJ, references update

Brown Dwarf Retrievals on FIRE!: Atmospheric Constraints and Lessons Learned from High Signal-to-Noise Medium Resolution Spectroscopy of a T9 Dwarf

Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Recently, atmospheric retrieval approaches have been applied to a number of low-resolution (R~100) spectra of brown dwarfs, yielding constraints on the abundances of chemical species and temperature structures of these atmospheres. Medium-resolution (R~1e3) spectra of brown dwarfs offer significant additional insight, as molecular features are more easily disentangled from one another and the thermal structure of the upper atmosphere is more readily probed. We present results from a GPU-based retrieval analysis of a high signal-to-noise, medium-resolution (R~6000) FIRE spectrum from 0.85-2.5 microns of a T9 dwarf. At 60x higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise. We examine the strong effect of different opacity sources on our retrieved constraints, in particular for CH4. Furthermore, we find that flaws in the data such as errors from order stitching can greatly bias our results. We compare these results to those obtained for a R~100 spectrum of the same object, revealing how constraints on atmospheric abundances and temperatures improve by an order of magnitude or more (depending on the species) with increased spectral resolution. In particular, we precisely constrain the abundance of H2S, which is undetectable at lower spectral resolution. While these medium-resolution retrievals offer the potential of precise, stellar-like constraints on atmospheric abundances (~0.02 dex), our retrieved radius is unphysically small (R~0.50 R$_{Jup}$), indicating lingering shortcomings with our modeling framework. This work is an initial investigation into brown dwarf retrievals at medium spectral resolution, offering guidance for future ground-based studies and JWST observations of substellar objects.Comment: 28 pages, 28 figures, 4 tables. Accepted to Ap

The Origin of Faint Tidal Features Around Galaxies in the RESOLVE Survey

We study tidal features (TFs) around galaxies in the REsolved Spectroscopy of a Local VolumE (RESOLVE) survey. Our sample consists of 1048 RESOLVE galaxies that overlap with the DECam Legacy Survey, which reaches an r-band 3σ depth of ∼27.9 mag arcsec−2 for a 100 arcsec2 feature. Images were masked, smoothed, and inspected for TFs like streams, shells, or tails/arms. We find TFs in 17±2% of our galaxies, setting a lower limit on the true frequency. The frequency of TFs in the gas-poor (gas-to-stellar mass ratio < 0.1) subsample is lower than in the gas-rich subsample (13±3% vs. 19±2%). Within the gas-poor subsample, galaxies with TFs have higher stellar and halo masses, ∼3× closer distances to nearest neighbors (in the same group), and possibly fewer group members at fixed halo mass than galaxies without TFs, but similar specific star formation rates. These results suggest TFs in gas-poor galaxies are typically streams/shells from dry mergers or satellite disruption. In contrast, the presence of TFs around gas-rich galaxies does not correlate with stellar or halo mass, suggesting these TFs are often tails/arms from resonant interactions. Similar to TFs in gas-poor galaxies, TFs in gas-rich galaxies imply 1.7x closer nearest neighbors in the same group; however, TFs in gas-rich galaxies are associated with diskier morphologies, higher star formation rates, and higher gas content. In addition to interactions with known neighbors, we suggest that TFs in gas-rich galaxies may arise from accretion of cosmic gas and/or gas-rich satellites below the survey limit

Detecting Water In the atmosphere of HR 8799 c with L-band High Dispersion Spectroscopy Aided By Adaptive Optics

High-dispersion spectroscopy of brown dwarfs and exoplanets enables exciting science cases, e.g., mapping surface inhomogeneity and measuring spin rate. Here, we present L-band observations of HR 8799 c using Keck NIRSPEC (R = 15,000) in adaptive optics (AO) mode (NIRSPAO). We search for molecular species (H_2O and CH_4) in the atmosphere of HR 8799 c with a template-matching method, which involves cross-correlation between reduced spectra and a template spectrum. We detect H_2O but not CH_4, which suggests disequilibrium chemistry in the atmosphere of HR 8799 c, and this is consistent with previous findings. We conduct planet signal injection simulations to estimate the sensitivity of our AO-aided high-dispersion spectroscopy observations. We conclude that 10^(−4) contrast can be reached in the L band. The sensitivity is mainly limited by the accuracy of line list used in modeling spectra and detector noise. The latter will be alleviated by the NIRSPEC upgrade

Prospects for Characterizing the Haziest Sub-Neptune Exoplanets with High Resolution Spectroscopy

Observations to characterize planets larger than Earth but smaller than Neptune have led to largely inconclusive interpretations at low spectral resolution due to hazes or clouds that obscure molecular features in their spectra. However, here we show that high-resolution spectroscopy (R $\sim$ 25,000 to 100,000) enables one to probe the regions in these atmospheres above the clouds where the cores of the strongest spectral lines are formed. We present models of transmission spectra for a suite of GJ1214b-like planets with thick photochemical hazes covering 1 - 5 $\mu$m at a range of resolutions relevant to current and future ground-based spectrographs. Furthermore, we compare the utility of the cross-correlation function that is typically used with a more formal likelihood-based approach, finding that only the likelihood based method is sensitive to the presence of haze opacity. We calculate the signal-to-noise of these spectra, including telluric contamination, required to robustly detect a host of molecules such as CO, CO$_{2}$, H$_{2}$O, and CH$_{4}$, and photochemical products like HCN, as a function of wavelength range and spectral resolution. Spectra in M band require the lowest S/N$_{res}$ to detect multiple molecules simultaneously. CH$_{4}$ is only observable for the coolest models ($T_{\rm{eff}} =$ 412 K) and only in the L band. We quantitatively assess how these requirements compare to what is achievable with current and future instruments, demonstrating that characterization of small cool worlds with ground-based high resolution spectroscopy is well within reach.Comment: Submitted to AAS Journals, revised to reflect referee comments. Posting of this manuscript on the arXiv was coordinated with S. Ghandi et a

Beyond Equilibrium Temperature: How the Atmosphere/Interior Connection Affects the Onset of Methane, Ammonia, and Clouds in Warm Transiting Giant Planets

The atmospheric pressure-temperature profiles for transiting giant planets cross a range of chemical transitions. Here we show that the particular shape of these irradiated profiles for warm giant planets below 1300 K lead to striking differences in the behavior of non-equilibrium chemistry compared to brown dwarfs of similar temperatures. Our particular focus is H$_2$O, CO, CH$_4$, CO$_2$, and NH$_3$ in Jupiter- and Neptune-class planets. We show the cooling history of a planet, which depends most significantly on planetary mass and age, can have a dominant effect on abundances in the visible atmosphere, often swamping trends one might expect based on Teq alone. The onset of detectable CH$_4$ in spectra can be delayed to lower Teq for some planets compared to equilibrium, or pushed to higher Teq. The detectability of NH$_3$ is typically enhanced compared to equilibrium expectations, which is opposite to the brown dwarf case. We find that both CH$_4$ and NH$_3$ can become detectable at around the same Teq (at Teq values that vary with mass and metallicity) whereas these "onset" temperatures are widely spaced for brown dwarfs. We suggest observational strategies to search for atmospheric trends and stress that non-equilibrium chemistry and clouds can serve as probes of atmospheric physics. As examples of atmospheric complexity, we assess three Neptune-class planets GJ 436b, GJ 3470b, and WASP-107, all around Teq=700 K. Tidal heating due to eccentricity damping in all three planets heats the deep atmosphere by thousands of degrees, and may explain the absence of CH$_4$ in these cool atmospheres. Atmospheric abundances must be interpreted in the context of physical characteristics of the planet.Comment: Accepted to AJ. No additional significant change

The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems II: A 1 to 20 Micron Spectrum of the Planetary-Mass Companion VHS 1256-1257 b

We present the highest fidelity spectrum to date of a planetary-mass object. VHS 1256 b is a $<$20 M$_\mathrm{Jup}$ widely separated ($\sim$8\arcsec, a = 150 au), young, planetary-mass companion that shares photometric colors and spectroscopic features with the directly imaged exoplanets HR 8799 c, d, and e. As an L-to-T transition object, VHS 1256 b exists along the region of the color-magnitude diagram where substellar atmospheres transition from cloudy to clear. We observed VHS 1256~b with \textit{JWST}'s NIRSpec IFU and MIRI MRS modes for coverage from 1 $\mu$m to 20 $\mu$m at resolutions of $\sim$1,000 - 3,700. Water, methane, carbon monoxide, carbon dioxide, sodium, and potassium are observed in several portions of the \textit{JWST} spectrum based on comparisons from template brown dwarf spectra, molecular opacities, and atmospheric models. The spectral shape of VHS 1256 b is influenced by disequilibrium chemistry and clouds. We directly detect silicate clouds, the first such detection reported for a planetary-mass companion.Comment: Accepted ApJL Iterations of spectra reduced by the ERS team are hosted at this link: https://github.com/bemiles/JWST_VHS1256b_Reduction/tree/main/reduced_spectr