Folded-port InfraRed Echellette Research Articles

Evidence for episodic black hole growth of reionization-era quasars observed with Magellan/FIRE

ABSTRACT Observations of high-redshift quasars hosting billion solar mass black holes at z ≳ 6 challenge our understanding of early supermassive black hole (SMBH) growth. In this work, we conduct a near-infrared spectroscopic study of 19 quasars at 6.2 ≲ z ≲ 7.5, using the Folded-port InfraRed Echellette instrument on the 6.5-m Magellan/Baade Telescope. We estimate the single-epoch masses of the quasars’ SMBHs by means of the Mg ii emission line and find black hole masses of $M_{\text{BH}} \approx (0.2\!\!-\!\!4.8)\, \times \, 10^9\ \mathrm{ M}_\odot$. Furthermore, we measure the sizes of the quasars’ proximity zones, which are regions of enhanced transmitted flux bluewards of the Ly $\alpha \,$ emission line, ionized by the quasars’ radiation itself. While it has been shown that the proximity zone sizes correlate with the quasars’ lifetimes due to the finite response time of the intergalactic medium to the quasars’ radiation, we do not find any correlation between the proximity zone sizes and the black hole mass, which suggests that quasar activity and the concomitant black hole growth are intermittent and episodic.

Staring at the Shadows of Archaic Galaxies: Damped Lyα and Metal Absorbers Toward a Young z ∼ 6 Weak-line Quasar

We characterize the Lyα halo and absorption systems toward PSO J083+11, a unique z = 6.3401 weak-line quasar, using Gemini Near-infrared Spectrograph, Magellan Folded-port Infrared Echellette, and Very Large Telescope Multi Unit Spectroscopic Explorer (MUSE) data. Strong absorptions by hydrogen and several metal lines (e.g., C ii, Mg ii, and O i) are discovered in the spectrum, which indicates the presence of: (i) a proximate subdamped Lyα (sub-DLA) system at z = 6.314 and (ii) a Mg ii absorber at z = 2.2305. To describe the observed damping wing signal, we model the Lyα absorption with a combination of a sub-DLA with the neutral hydrogen column density of and absorption from the intergalactic medium with a neutral fraction of around 10%. The sub-DLA toward PSO J083+11 has an abundance ratio of [C/O] = −0.04 ± 0.33 and metallicity of [O/H] = −2.19 ± 0.44, similar to those of low-redshift metal-poor DLAs. These measurements suggest that the sub-DLA might truncate PSO J083+11’s proximity zone size and complicate the quasar lifetime measurement. However, this quasar shows no sign of a Lyα halo in the MUSE data cube, where the estimated 1σ limit of surface brightness is at an aperture size of 1″, or equivalent to a Lyα luminosity of ≤43.46 erg s−1. This nondetection, while being only weak independent evidence on its own, is at least consistent with a young quasar scenario, as expected for a quasar with a short accretion timescale.

Near-infrared spectroscopy of extreme BAL QSOs from the QUBRICS bright quasar survey

ABSTRACT We report on the spectral confirmation of 18 quasi-stellar object (QSO) candidates from the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) survey, previously observed in the optical band, for which we acquired new spectroscopic data in the near-infrared band with the Folded-port InfraRed Echellette (FIRE) spectrograph at the Magellan Baade telescope. In most cases, further observations were prompted by the peculiar nature of the targets, whose optical spectra displayed unexpected absorption features. All candidates have been confirmed as bona fide QSOs, with average emission redshift z ≃ 2.1. The analysis of the emission and absorption features in the spectra, performed with astrocook and QSFit, reveals that the large majority of these objects are broad absorption line (BAL) QSOs, with almost half of them displaying strong Fe ii absorption (typical of the so-called FeLoBAL QSOs). The detection of such a large fraction of rare objects (which are estimated to account for less than 1 per cent of the general QSO population) is interpreted as an unexpected (yet favourable) consequence of the particular candidate selection procedure adopted within the QUBRICS survey. The measured properties of FeLoBAL QSOs observed so far provide no evidence that they are a manifestation of a particular stage in active galactic nucleus (AGN) evolution. In this paper, we present an explorative analysis of the individual QSOs, to serve as a basis for a further, more detailed investigation.

RELICS: spectroscopy of gravitationally lensed z ≃ 2 reionization-era analogues and implications for C iii] detections at z > 6

ABSTRACT Recent observations have revealed the presence of strong C iii] emission (EW$_{\rm {C\,{\small III}]}}\gt 20$ Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line emitters, we have initiated a survey targeting C iii] emission in gravitationally lensed reionization-era analogues identified in Hubble Space Telescope imaging of clusters from the Reionization Lensing Cluster Survey. Here, we report initial results on four galaxies selected to have low stellar masses (2–8 × 107 M⊙) and J125-band flux excesses indicative of intense [O iii] + H β emission (EW$_{\rm {[O\,{\small III}]+H\,\beta }}$ = 500–2000 Å), similar to what has been observed at z > 6. We detect C iii] emission in three of the four sources, with the C iii] EW reaching values seen in the reionization era (EW$_{\rm {C\,{\small III}]}}\simeq 17\!-\!22$ Å) in the two sources with the strongest optical line emission (EW$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$ Å). We have obtained a Magellan/FIRE (Folded-port InfraRed Echellette) near-infrared spectrum of the strongest C iii] emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense C iii] and optical line emission for extremely young (2–3 Myr) and metal-poor (0.06–0.08 Z⊙) stellar populations, as would be expected after a substantial upturn in the star formation rate of a low-mass galaxy. The sources in this survey are among the first for which C iii] has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using C iii] to measure redshifts of objects with IRAC excesses indicating EW$_{\rm {[O\,{\small III}]+H\,\beta }}\simeq 2000$ Å, providing a method of spectroscopic confirmation independent of Ly α.

WISE 2150-7520AB: A Very Low-mass, Wide Comoving Brown Dwarf System Discovered through the Citizen Science Project Backyard Worlds: Planet 9*

Abstract We report the discovery of WISE 2150-7520AB (W2150AB): a widely separated (∼341 au) very low-mass L1 + T8 co-moving system. The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99–75:20:54.6 (MJD = 57947) using Wide-field Infrared Survey Explorer data via the Backyard Worlds: Planet 9 citizen science project. We present Spitzer ch1 and ch2 photometry (ch1–ch2 = 1.41 ± 0.04 mag) of the secondary and Folded-port InfraRed Echellette prism spectra of both components. The sources show no peculiar spectral or photometric signatures, indicating that each component is likely field age. Using all observed data and the Gaia DR2 parallax of 41.3593 ± 0.2799 mas for W2150A we deduce fundamental parameters of log(L bol/L ☉) = −3.69 ± 0.01, T eff = 2118 ± 62 K, and an estimated mass = 72 ± 12 M Jup for the L1 and log(L bol/L ☉) = −5.64 ± 0.02, T eff = 719 ± 61 K, and an estimated mass = 34 ± 22 M Jup for the T8. At a physical separation of ∼341 au this system has E bin = 1041 erg, making it the lowest binding energy system of any pair with M tot < 0.1 M Sun not associated with a young cluster. It is equivalent in estimated mass ratio, E bin, and physical separation to the ∼2 Myr M7.25 + M8.25 binary brown dwarf 2MASS J11011926-7732383AB (2M1101AB) found in the Chameleon star-forming region. W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later.

A Reanalysis of the Fundamental Parameters and Age of TRAPPIST-1*

Abstract We present the distance-calibrated spectral energy distribution (SED) of TRAPPIST-1 using a new medium-resolution (R ∼ 6000) near-infrared (NIR) Folded-port InfraRed Echellette (FIRE) spectrum and its Gaia parallax. We report an updated bolometric luminosity (L bol) of −3.216 ± 0.016, along with semiempirical fundamental parameters: effective temperature T eff = 2628 ± 42 K, mass = 90 ± 8 M Jup, radius = 1.16 ± 0.03 R Jup, and log g = 5.21 ± 0.06 dex. Its kinematics point toward an older age, while spectral indices indicate youth; therefore, we compare the overall SED and NIR bands of TRAPPIST-1 to field-age, low-gravity, and low-metallicity dwarfs of similar T eff and L bol. We find field dwarfs of similar T eff and L bol best fit the overall and band-by-band features of TRAPPIST-1. Additionally, we present new Allers & Liu spectral indices for the SpeX SXD and FIRE spectra of TRAPPIST-1, both classifying it as intermediate gravity. Examining T eff, L bol, and absolute JHKW1W2 magnitudes versus optical spectral type places TRAPPIST-1 in an ambiguous location containing both field and intermediate-gravity sources. Kinematics place TRAPPIST-1 within a subpopulation of intermediate-gravity sources lacking bona fide membership in a moving group with higher tangential and UVW velocities. We conclude that TRAPPIST-1 is a field-age source with subtle spectral features reminiscent of a low surface gravity object. To resolve the cause of TRAPPIST-1's intermediate-gravity indicators we speculate on two avenues that might be correlated to inflate the radius: (1) magnetic activity or (2) tidal interactions from planets. We find the M8 dwarf LHS 132 is an excellent match to TRAPPIST-1's spectral peculiarities along with the M9 β dwarf 2MASS J10220489+0200477, the L1 β 2MASS J10224821+5825453, and the L0 β 2MASS J23224684−3133231, which have distinct kinematics, making all four intriguing targets for future exoplanet studies.

Evidence of a Bottom-heavy Initial Mass Function in Massive Early-type Galaxies from Near-infrared Metal Lines*

Abstract We present new evidence for a variable stellar initial mass function (IMF) in massive early-type galaxies, using high-resolution, near-infrared spectroscopy from the Folded-port InfraRed Echellette spectrograph (FIRE) on the Magellan Baade Telescope at Las Campanas Observatory. In this pilot study, we observe several gravity-sensitive metal lines between 1.1 and 1.3 μm in eight highly luminous ( ) nearby galaxies. Thanks to the broad wavelength coverage of FIRE, we are also able to observe the Ca ii triplet feature, which helps with our analysis. After measuring the equivalent widths (EWs) of these lines, we notice mild to moderate trends between EW and central velocity dispersion (σ), with some species (K i, Na i, Mn i) showing a positive EW–σ correlation and others (Mg i, Ca ii, Fe i) a negative one. To minimize the effects of metallicity, we measure the ratio R = [EW(K i)/EW(Mg i)], finding a significant systematic increase in this ratio with respect to σ. We then probe for variations in the IMF by comparing the measured line ratios to the values expected in several IMF models. Overall, we find that low-mass galaxies ( km s−1) favor a Chabrier IMF, while high-mass galaxies ( km s−1) are better described with a steeper (dwarf-rich) IMF slope. While we note that our galaxy sample is small and may suffer from selection effects, these initial results are still promising. A larger sample of galaxies will therefore provide an even clearer picture of IMF trends in this regime.

A Calibrated Measurement of the Near-IR Continuum Sky Brightness Using Magellan/FIRE

ABSTRACTWe characterize the near-IR sky background from 308 observations with the Folded-port InfraRed Echellette (FIRE) spectrograph at Magellan. A subset of 105 observations selected to minimize lunar and thermal effects gives a continuous, median spectrum from 0.83 to 2.5 μm, which we present in Table 2. The data are used to characterize the broadband continuum emission between atmospheric OH features and correlate its properties with observing conditions such as lunar angle and time of night. We find that the Moon contributes significantly to the inter-line continuum in Y and J bands, whereas the observed H-band continuum is dominated by the blended Lorentzian wings of multiple OH line profiles, even at R = 6000. Lunar effects may be mitigated in Y and J through careful scheduling of observations, but the most ambitious near-IR programs will benefit from allocation during dark observing time if those observations are not limited by read noise. In Y and J, our measured continuum exceeds space-based average estimates of the zodiacal light, but it is not readily identified with known terrestrial foregrounds. If further measurements confirm such a fundamental background, it would impact requirements for OH-suppressed instruments operating in this regime.

FIRE SPECTROSCOPY OF FIVE LATE-TYPE T DWARFS DISCOVERED WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER

We present the discovery of five late-type T dwarfs identified with the Wide-field Infrared Survey Explorer (WISE). Low-resolution near-infrared spectroscopy obtained with the Magellan Folded-port InfraRed Echellette reveal strong H2O and CH4 absorption in all five sources, and spectral indices and comparison to spectral templates indicate classifications ranging from T5.5 to T8.5:. The spectrum of the latest-type source, WISE J1812+2721, is an excellent match to that of the T8.5 companion brown dwarf Wolf 940B. WISE-based spectrophotometric distance estimates place these T dwarfs at 12–13 pc from the Sun, assuming they are single. Preliminary fits of the spectral data to the atmosphere models of Saumon & Marley indicate effective temperatures ranging from 600 K to 930 K, both cloudy and cloud-free atmospheres, and a broad range of ages and masses. In particular, two sources show evidence of both low surface gravity and cloudy atmospheres, tentatively supporting a trend noted in other young brown dwarfs and exoplanets. In contrast, the high proper motion T dwarf WISE J2018−7423 exhibits a suppressed K-band peak and blue spectrophotometric J − K colors indicative of an old, massive brown dwarf; however, it lacks the broadened Y-band peak seen in metal-poor counterparts. These results illustrate the broad diversity of low-temperature brown dwarfs that will be uncovered with WISE.

CLOUDS IN THE COLDEST BROWN DWARFS: FIRE SPECTROSCOPY OF ROSS 458C

Condensate clouds are a salient feature of L dwarf atmospheres, but have been assumed to play little role in shaping the spectra of the coldest T-type brown dwarfs. Here we report evidence of condensate opacity in the near-infrared spectrum of the brown dwarf candidate Ross 458C, obtained with the Folded-Port Infrared Echellette (FIRE) spectrograph at the Magellan Telescopes. These data verify the low-temperature nature of this source, indicating a T8 spectral classification, log Lbol/Lsun = -5.62+/-0.03, Teff = 650+/-25 K, and a mass at or below the deuterium burning limit. The data also reveal enhanced emission at K-band associated with youth (low surface gravity) and supersolar metallicity, reflecting the properties of the Ross 458 system (age = 150-800 Myr, [Fe/H] = +0.2 to +0.3). We present fits of FIRE data for Ross 458C, the T9 dwarf ULAS J133553.45+113005.2, and the blue T7.5 dwarf SDSS J141624.08+134826.7B, to cloudless and cloudy spectral models from Saumon & Marley. For Ross 458C we confirm a low surface gravity and supersolar metallicity, while the temperature differs depending on the presence (635 [+25,-35] K) or absence (760 [+70,-45] K) of cloud extinction. ULAS J1335+1130 and SDSS J1416+1348B have similar temperatures (595 [+25,-45] K), but distinct surface gravities (log g = 4.0-4.5 cgs versus 5.0-5.5 cgs) and metallicities ([M/H] ~ +0.2 versus -0.2). In all three cases, cloudy models provide better fits to the spectral data, significantly so for Ross 458C. These results indicate that clouds are an important opacity source in the spectra of young cold T dwarfs, and should be considered when characterizing the spectra of planetary-mass objects in young clusters and directly-imaged exoplanets. The characteristics of Ross 458C suggest it could itself be regarded as a planet, albeit one whose cosmogony does not conform with current planet formation theories.