Eureka Scientific

Abstract The Massive and Distant Clusters of Wide-field Infrared Survey Explorer (WISE) Survey 2 (MaDCoWS2) is a WISE-selected catalog of galaxy clusters at 0.1 &lt; z &lt; 2 covering an effective area of &gt;6000 deg 2 . In this paper, we derive splashback radii for this cluster ensemble from galaxy density profiles and constrain the mass threshold of the survey as a function of redshift. We use MaDCoWS2 cluster candidates at 0.4 ≤ z ≤ 1.65 divided into subsamples with different Poissonian signal-to-noise ratios (S/N P s) and redshifts, cross correlated with galaxies from the CatWISE2020 catalog, to obtain average surface density profiles. We perform a Markov Chain Monte Carlo analysis to derive parameter estimates for theoretical models consisting of orbiting and infalling terms. A distinct splashback feature is detected in all subsamples. The measured splashback radii span from <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.8</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> cMpc ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.6</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.02</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> pMpc) at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>0.45</mml:mn> </mml:math> to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>1.2</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>7</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.05</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> cMpc ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>0.5</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.04</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.04</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mi>h</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> pMpc) at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>z</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">¯</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:mn>1.54</mml:mn> </mml:math> . We also find that the splashback radii increase with S/N P at fixed redshift. The resultant splashback radii constrain the redshift dependence of the mass of MaDCoWS2 clusters at fixed S/N P . We calculate M 200m from the radii using a relation based on a cosmological simulation. MaDCoWS2 M 200m values derived from the simulation-based relation are lower than the expected values based on weak-lensing observations. More robust mass constraints will come from calibrating splashback radii derived from galaxy density profiles with weak-lensing shear profiles from facilities such as Euclid, the Vera C. Rubin Observatory, and the Nancy Grace Roman Space Telescope.

Abstract Accurate pulsar astrometric estimates are essential to almost all high-precision pulsar timing experiments. Traditional pulsar timing techniques refine these estimates by including them as free parameters when fitting a model to observed pulse time-of-arrival measurements. However, reliable submilliarcsecond astrometric estimations require years of observations. Even then, power from red noise can be inadvertently absorbed into astrometric parameter fits. This effect biases the resulting estimates and reduces the sensitivity to red noise processes, including gravitational waves (GWs). In this work, we seek to mitigate these shortcomings by using pulsar astrometric estimates derived from very long baseline interferometry (VLBI) as priors for the timing fit. First, we used VLBI and timing astrometric estimates of 18 millisecond pulsars to calibrate a rotation between the reference frames used in timing and VLBI, with a precision of ∼0.7 mas. Through this frame tie, we combined timing- and VLBI-based probabilities to obtain a maximum-posterior astrometric solution. We found offsets between our results and the timing-based astrometric solutions, which, if real, would lead to the absorption of spectral power at the frequencies of interest for single-source GW searches. However, we do not find significant power absorption due to astrometric fitting at the low-frequency domain of the GW background.

Changing-state active galactic nuclei (CSAGNs) exhibit rapid variability; their mass accretion rates can change by several orders of magnitude in a few years. This provides us with a unique opportunity to study the evolution of the inner accretion flow almost in real time. Here we used over 1000 observations to study the broadband X-ray spectra of a sample of five CSAGNs, spanning three orders of magnitude in Eddington ratio ( λ Edd ), using phenomenological models to trace the evolution of key spectral components. We derive several fundamental parameters, such as the photon index, soft excess strength, reflection strength, and luminosities of the soft excess and primary continuum. We find that the soft excess and primary continuum emissions show a very strong positive correlation ( p ≪ 10 −10 ), suggesting a common physical origin. The soft excess strength does not show any dependence on the reflection parameter, suggesting that in these objects the soft excess is not dominated by a blurred ionized reflection process. On the other hand, the strength of the soft excess is found to be strongly positively correlated with the Eddington ratio ( p ≪ 10 −10 ), and we find that the soft excess vanishes below log λ Edd ∼ −2.5. Moreover, we find a clear V-shaped relation for Γ − λ Edd , with a break at log λ Edd = −2.47 ± 0.09. Our findings indicate a change in the geometry of the inner accretion flow at low Eddington ratios, and that the soft excess is primarily produced via warm Comptonization.

Abstract We present proper motion (PM) measurements for Draco II, an ultrafaint dwarf satellite of the Milky Way. These PMs are measured using two epochs of Hubble Space Telescope (HST)/Advanced Camera for Surveys imaging separated by a 7 yr temporal baseline. Measuring the PMs of low-luminosity systems is difficult due to the low number of member stars, requiring a precise inertial reference frame. We construct reference frames using three different sets of external sources: (1) stars with Gaia Data Release 3 data, (2) stationary background galaxies, and (3) a combination of the two. We show that all three reference frames give consistent PM results. We find that for this sparse, low-luminosity regime including background galaxies into the reference frame improves our measurement by up to ∼2× versus using only Gaia astrometric data. Using 301 background galaxies as a reference frame, we find that Draco II’s systemic PM is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msubsup> <mml:mo>,</mml:mo> <mml:msub> <mml:mrow> <mml:mi>μ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>δ</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1.043</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.029</mml:mn> <mml:mo>,</mml:mo> <mml:mn>0.879</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.028</mml:mn> <mml:mo stretchy="false">)</mml:mo> </mml:math> mas yr −1 , which is the most precise measurement of the three we present in this paper.

Abstract Motivated by a number of X-ray observations of active galactic nuclei (AGNs) that exhibit a potential signature of ultrafast inflows (UFIs), we consider in this work a scenario that UFIs can be physically identified as weakly magnetized hydrodynamic accretion flows that are guided and channeled by a poloidal magnetic field into low-to-mid-latitude above the equatorial disk. In the context of general relativistic hydrodynamics (GRHD) under a weak-field limit in Kerr spacetime, we present a set of preliminary results by numerically calculating the physical property of GRHD flows (e.g., kinematics and density distribution) in an effort to simulate redshifted absorption line spectra. Our model demonstrates that such GRHD accretion off the equatorial plane (i.e., v ≳ 0.1 c where c is the speed of light in the vicinity of AGN closer than ∼100 Schwarzschild radii) can manifest itself as UFIs in the form of a redshifted absorption signature assuming the observed characteristics such as column density of N H ∼ 10 23 cm −2 and ionization parameter of log ( ξ [ erg cm s − 1 ] ) ∼ 3 , as also seen in recent multiepoch NuSTAR observations among other data.

Abstract Free-floating objects (FFOs) in interstellar space—rogue planets, brown dwarfs, and large asteroids that are not gravitationally bound to any star—are expected to be ubiquitous throughout the Milky Way. Recent microlensing surveys have discovered several free-floating planets that are not bound to any known stellar systems. Additionally, three interstellar objects, namely 1I/’Oumuamua, 2I/Borisov, and 3I/ATLAS, have been detected passing through our solar system on hyperbolic trajectories. In this work, we search for FFOs on hyperbolic orbits that pass near millisecond pulsars (MSPs), where their gravitational influence can induce detectable perturbations in pulse arrival times. Using the NANOGrav 15 yr narrow band dataset, which contains high-precision timing data for 68 MSPs, we conduct a search for such hyperbolic scattering events between FFOs and pulsars. Although no statistically significant events were detected, this nondetection enables us to place upper limits (ULs) on the number density of FFOs as a function of their mass within our local region of the Galaxy. For example, the UL on the number density for Jupiter-mass FFOs (∼10 −2.5 –10 −3.5 M ⊙ ) obtained from different pulsars ranges from 5.25 × 10 6 pc −3 to 5.37 × 10 9 pc −3 , while the UL calculated by combining results from all the pulsars is 6.03 × 10 5 pc −3 . These results represent the first constraints on FFO population derived from pulsar timing data.

Abstract Radiation pressure on spectral lines is a promising mechanism for powering disc winds from accreting white dwarfs (AWDs) and active galactic nuclei (AGN). However, in radiation-hydrodynamic simulations, overionization reduces line opacity and quenches the line force, which suppresses outflows. Here, we show that small-scale clumping can resolve this problem. Adopting the microclumping approximation, our new simulations demonstrate that even modest volume filling factors (fV ∼ 0.1–0.01) can dramatically increase the wind mass-loss rate by lowering its ionization state—raising $\dot{M}_{\rm wind}$ and yielding $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}\!\gtrsim \!10^{-4}$ for such modest filling factors. Clumpy wind models produce the UV resonance lines that are absent from smooth wind models. They can also reprocess a significant fraction of the disc luminosity and thus dramatically modify the broad-band optical/UV SED. Given that theory and observations indicate that disc winds are intrinsically inhomogeneous, clumping offers a physically motivated solution. Together, these results provide the first robust, self-consistent demonstration that clumping can reconcile line-driven wind theory with observations across AWDs and AGNs.

Abstract We performed the first simultaneous NICER and NuSTAR spectral and timing study of the Sco-like Z source GX 17+2. The source traced the full Z track during four observations. We detect signatures of relativistic reflection in the broadband spectra and report results using a reflection framework. The disk is relatively close to the innermost stable circular orbit (∼1 R ISCO –4 R ISCO ), which agrees with previous studies of GX 17+2, but the location of the inner disk is farther out in the horizontal branch (HB) and moves inward toward the flaring branch (FB). We find the FB to be the point of closest approach of the disk to the neutron star. We qualitatively conclude that the evolution of the source along the hardness intensity diagram (HID) is that of a relatively truncated disk in the HB (∼4 R ISCO ) that approaches the neutron star as it goes along the HID toward the normal branch (NB), soft apex (SA), and finally the FB. We attribute the source evolution along the Z track to varying mass accretion rate and disk instabilities. The rms variability increases from the NB toward the SA and then drops to a constant along the FB, indicating that the observed variability likely originates from the disk/boundary layer rather than the corona.

Abstract It is commonly supposed that quenched field dwarfs near the edge of the Local Group (LG) are backsplash galaxies, having previously orbited within the Milky Way (MW) or M31’s virial radius, whereas galaxies on first infall should still have gas and star formation. We measured proper motions (PMs) for six dwarf galaxies located 400–1000 kpc from the MW using the Hubble Space Telescope. For four galaxies (Aquarius, Cetus, Pisces, and Tucana), we report the first PMs. For the remaining two (Leo T and Pegasus), we measure PMs with order-of-magnitude precision improvement. We compute orbital histories to assess whether any of the six are backsplash galaxies. While some have nonzero likelihoods of past interaction with the MW or M31, these are weak and typically occur at large distances (i.e., &gt;2 R vir ). The properties of Aquarius, Leo T, Pisces, and Pegasus are consistent with first passage through a massive halo. Cetus, which shows a low probability (∼4%–6%) of interacting with the MW or M31 in the last 6 Gyr, is more likely a backsplash galaxy resulting from an interaction with M31 over 6 Gyr ago, in the regime where rigid orbital models become less reliable. Tucana has been thought to be a backsplash galaxy, but our orbits indicate it cannot have interacted with a massive LG host. Our results highlight the diversity of evolutionary pathways for isolated, intermediate-mass dwarfs ( M * ≈ 10 5 –10 7 M ⊙ ) and the need to reassess quenching mechanisms beyond environmental interactions with massive hosts.

Abstract We use the narrow [Ne v] λ3427 emission line detected in the recently published JWST spectra of two galaxies, at z ≃ 6.9 and 5.6, to study the key properties of the active galactic nuclei (AGN) and the supermassive black holes (SMBHs) in their centers. Using a new empirical scaling linking the Ne V line emission with AGN accretion-driven (continuum) emission, derived from a highly complete low-redshift AGN sample, we show that the Ne V emission in the two z &gt; 5 galaxies implies total (bolometric) AGN luminosities of order L bol ≈ (4–8) × 1045 erg s−1. Assuming that the radiation emitted from these systems is Eddington limited, the (minimal) black hole (BH) masses are of order M BH ≳ 107 M ⊙. Combined with the published stellar masses of the galaxies, estimated from dedicated fitting of their spectral energy distributions, the implied BH-to-stellar mass ratios are of order M BH/M host ≈ 0.1–1. This is considerably higher than what is found in the local Universe, but is consistent with the general trend seen in some other z ≳ 5 AGN. Given the intrinsic weakness of the Ne V line and the nature of the Ne V –to–L bol scaling, any (rare) detection of the [Ne v] λ3427 line at z &gt; 5 would translate to similarly high AGN luminosities and SMBH masses, thus providing a unique observational path for studying luminous AGN well into the epoch of reionization, including obscured sources.