Radius Of Re Research Articles

Homoleptic Rare-Earth-Metal Sandwiches with Dibenzo[a,e]cyclooctatetraene Dianions.

A family of rare-earth complexes [RE(III) = Y, La, Gd, Tb, Dy, and Er] with doubly reduced dibenzo[a,e]cyclooctatetraene (DBCOT) has been synthesized and structurally characterized. X-ray diffraction analysis confirms that all products of the [RE(DBCOT)(THF)4][RE(DBCOT)2] composition consist of the anionic sandwich [RE(DBCOT)2]- and the cationic counterpart [RE(DBCOT)(THF)4]+. Within the sandwich, two elongated π decks are slightly bent toward the metal center (avg. 7.3°) with a rotation angle of 35.9-37.6°. The RE(III) ion is entrapped between the central eight-membered rings of DBCOT2- in a η8 fashion. The trends in the RE-COT bond lengths are consistent with the variations of the ionic radii of RE(III) centers. The 1H NMR spectra of the diamagnetic Y(III) and La(III) analogues illustrate the distinct solution behavior for the cationic and anionic parts in this series. Magnetic measurements for the Dy analogue reveal single-molecule magnetism, which was rationalized by considering the effect of crystal-field splitting for both building units analyzed by electronic structure calculations.

An almost dark galaxy with the mass of the Small Magellanic Cloud

Almost dark galaxies are objects that have eluded detection by traditional surveys such as the Sloan Digital Sky Survey (SDSS). The low surface brightness of these galaxies (μr(0) > 26 mag arcsec−2), and hence their low surface stellar mass density (a few solar masses per pc2 or less), suggest that the energy density released by baryonic feedback mechanisms is inefficient in modifying the distribution of the dark matter halos they inhabit. For this reason, almost dark galaxies are particularly promising for probing the microphysical nature of dark matter. In this paper, we present the serendipitous discovery of Nube, an almost dark galaxy with ⟨μV⟩e ∼ 26.7 mag arcsec−2. The galaxy was identified using deep optical imaging from the IAC Stripe82 Legacy Project. Follow-up observations with the 100 m Green Bank Telescope strongly suggest that the galaxy is at a distance of 107 Mpc. Ultra-deep multi-band observations with the 10.4 m Gran Telescopio Canarias favour an age of ∼10 Gyr and a metallicity of [Fe/H] ∼ −1.1. With a stellar mass of ∼4 × 108 M⊙ and a half-mass radius of Re = 6.9 kpc (corresponding to an effective surface density of ⟨Σ⟩e ∼ 0.9 M⊙ pc−2), Nube is the most massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger than typical ultradiffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local Group have very low mass (tens of 105 M⊙) and compact structures (effective radius Re < 1 kpc). Current cosmological simulations within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube. However, its highly extended and flattened structure is consistent with a scenario where the dark matter particles are ultralight axions with a mass of mB = (0.8−0.2+0.4) × 10−23 eV.

A variable active galactic nucleus at z = 2.06 triply-imaged by the galaxy cluster MACS J0035.4−2015

ABSTRACT We report the discovery of a triply imaged active galactic nucleus (AGN), lensed by the galaxy cluster MACS J0035.4−2015 (zd = 0.352). The object is detected in Hubble Space Telescope imaging taken for the RELICS program. It appears to have a quasi-stellar nucleus consistent with a point-source, with a de-magnified radius of re ≲ 100 pc. The object is spectroscopically confirmed to be an AGN at zspec = 2.063 ± 0.005 showing broad rest-frame UV emission lines, and detected in both X-ray observations with Chandra and in ALCS ALMA band 6 (1.2 mm) imaging. It has a relatively faint rest-frame UV luminosity for a quasar-like object, MUV, 1450 = −19.7 ± 0.2. The object adds to just a few quasars or other X-ray sources known to be multiply lensed by a galaxy cluster. Some diffuse emission from the host galaxy is faintly seen around the nucleus, and there is a faint object nearby sharing the same multiple-imaging symmetry and geometric redshift, possibly an interacting galaxy or a star-forming knot in the host. We present an accompanying lens model, calculate the magnifications and time delays, and infer the physical properties of the source. We find the rest-frame UV continuum and emission lines to be dominated by the AGN, and the optical emission to be dominated by the host galaxy of modest stellar mass $M_{\star }\simeq 10^{9.2}\, \mathrm{M}_{\odot }$ . We also observe some variation in the AGN emission with time, which may suggest that the AGN used to be more active. This object adds a low-redshift counterpart to several relatively faint AGN recently uncovered at high redshifts with HST and JWST.

Influence of average radii of RE3+ions on phase structures and thermal expansion coefficients of high-entropy pyrosilicates

High-entropy pyrosilicate element selection is relatively blind, and the thermal expansion coefficient (CTE) of traditional β-type pyrosilicate is not adjustable, making it difficult to meet the requirements of various types of ceramic matrix composites (CMCs). The following study aimed to develop a universal rule for high-entropy pyrosilicate element selection and to achieve directional control of the thermal expansion coefficient of high-entropy pyrosilicate. The current study investigates a high-entropy design method for obtaining pyrosilicates with stable β-phase and γ-phase by introducing various rare-earth (RE) cations. The solid-phase method was used to create 12 different types of high-entropy pyrosilicates with 4–6 components. The high-entropy pyrosilicates gradually transformed from β-phase to γ-phase with an increase in the average radius of RE³⁺ ions (<inline-formula> <math display="inline" id="MA1"><mrow><mover accent="true"><mi>r</mi><mo>¯</mo></mover><mo stretchy="false">(</mo><msup><mrow><mtext>RE</mtext></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup><mo stretchy="false">)</mo></mrow></math></inline-formula>). The nine pyrosilicates with a small <inline-formula> <math display="inline" id="MA2"><mrow><mover accent="true"><mi>r</mi><mo>¯</mo></mover><mo stretchy="false">(</mo><msup><mrow><mtext>RE</mtext></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup><mo stretchy="false">)</mo></mrow></math></inline-formula> preserve β-phase or γ-phase stability at room temperature to the maximum of 1400 ℃. The intrinsic relationship between the thermal expansion coefficient, phase structure, and RE–O bond length has also been found. This study provides the theoretical background for designing high-entropy pyrosilicates from the perspective of <inline-formula> <math display="inline" id="MA3"><mrow><mover accent="true"><mi>r</mi><mo>¯</mo></mover><mo stretchy="false">(</mo><msup><mrow><mtext>RE</mtext></mrow><mrow><mn>3</mn><mo>+</mo></mrow></msup><mo stretchy="false">)</mo></mrow></math></inline-formula>. The theoretical guidance makes it easier to synthesize high-entropy pyrosilicates with stable β-phase or γ-phase for the use in environmental barrier coatings (EBCs). The thermal expansion coefficient of γ-type high-entropy pyrosilicate can be altered through component design to match various types of CMCs.

Growth of REBa2Cu3O x single-crystal whiskers utilizing the concept of high-entropy alloys

Single-crystal whiskers of REBa2Cu3O x (RE-123, RE: rare Earth element) cuprate superconductors were successfully grown using Te-doped precursors utilizing the concept of high-entropy-alloys at the RE site. The obtained whiskers were 0.5–1.0 mm in length with approximately 10 μm thickness. The width of the flat surface, which corresponds to the ab-plane, was 10–50 μm. The RE site of the grown whiskers could be easily substituted by large ionic radius RE elements (Gd, Dy and Ho). Substitution with small ionic radius RE elements (Tm, Yb and Lu) resulted in the opposite trend. The superconducting transition temperature and superconducting anisotropy of the grown RE-123 whiskers were 89–93 K and 6–10, respectively. The mixed entropy at the RE site in the RE-123 whiskers did not affect the superconducting transition temperature and superconducting anisotropy.

GOODS-ALMA 2.0: Source catalog, number counts, and prevailing compact sizes in 1.1 mm galaxies

Submillimeter/millimeter observations of dusty star-forming galaxies with the Atacama Large Millimeter/submillimeter Array (ALMA) have shown that dust continuum emission generally occurs in compact regions smaller than the stellar distribution. However, it remains to be understood how systematic these findings are. Studies often lack homogeneity in the sample selection, target discontinuous areas with inhomogeneous sensitivities, and suffer from modest uv coverage coming from single array configurations. GOODS-ALMA is a 1.1 mm galaxy survey over a continuous area of 72.42 arcmin2 at a homogeneous sensitivity. In this version 2.0, we present a new low resolution dataset and its combination with the previous high resolution dataset from the survey, improving the uv coverage and sensitivity reaching an average of σ = 68.4 μJy beam−1. A total of 88 galaxies are detected in a blind search (compared to 35 in the high resolution dataset alone), 50% at S/Npeak ≥ 5 and 50% at 3.5 ≤ S/Npeak ≤ 5 aided by priors. Among them, 13 out of the 88 are optically dark or faint sources (H- or K-band dropouts). The sample dust continuum sizes at 1.1 mm are generally compact, with a median effective radius of Re = 0.″10 ± 0.″05 (a physical size of Re = 0.73 ± 0.29 kpc at the redshift of each source). Dust continuum sizes evolve with redshift and stellar mass resembling the trends of the stellar sizes measured at optical wavelengths, albeit a lower normalization compared to those of late-type galaxies. We conclude that for sources with flux densities S1.1 mm &gt; 1 mJy, compact dust continuum emission at 1.1 mm prevails, and sizes as extended as typical star-forming stellar disks are rare. The S1.1 mm &lt; 1 mJy sources appear slightly more extended at 1.1 mm, although they are still generally compact below the sizes of typical star-forming stellar disks.

Subaru/FOCAS IFU revealed the metallicity gradient of a local extremely metal-poor galaxy

Abstract We present the first measurement of the metallicity gradient in extremely metal-poor galaxies (EMPGs). With Subaru/Faint Object Camera And Spectrograph (FOCAS) Integral Field Unit (IFU), we have observed a nearby, low-mass EMPG, HSC J1631+4426, whose oxygen abundance and stellar mass are known to be 12 + log (O/H) = 6.9 and log10(M*/M⊙) = 5.8, respectively. The measured metallicity gradient is −0.36 ± 0.04 dex kpc−1 corresponding to −0.049 ± 0.006 dex$\:R_\mathrm{e}^{-1}$ for the continuum effective radius of Re = 0.14 kpc. Our observation has successfully demonstrated that three-dimensional spectroscopy with 8 m-class telescopes is powerful enough to reveal the metallicity distribution in local EMPGs, providing precious information on the baryon cycle in local analogs of primordial galaxies in the early Universe.

The involvement of Pna21 phase in the multiferroic characteristics of La/Lu co-substituted BiFeO3 ceramics

Rare earth ion (RE)-substitution has been recognized as an effective way for improving multiferroic properties especially for realizing the electric field-controlled magnetism in BiFeO3 ceramics, where the symmetry modulation of R3c-Pna21-Pbnm and unlocking ferromagnetism by destroying the cycloidal spin structure are the key points. In Lu-substituted BiFeO3 ceramics, however, the Pna21 phase is not involved. In the present work, La/Lu co-substitution was investigated to involve the Pna21 phase in BiFeO3 ceramics. The phase transition from R3c to Pna21 occurred with an increase in x, and the mixed structure of R3c, Pna21, and Pbnm phases was determined in Bi0.82−xLaxLu0.18FeO3 ceramics. The greatly enhanced ferroelectric polarization and the switching from antiferromagnetic to the weak ferromagnetic state through the destruction of the cycloidal spin structure were achieved. Subsequently, the direct magnetoelectric coupling coefficient αME up to 2.02 mV/cm Oe was obtained. The increased effective ionic radius of RE in the present ceramics played a key role in involving Pna21 phase in RE-substituted BiFeO3 ceramics, and the critical value was about 0.104 23(2) nm.

EMPRESS. III. Morphology, Stellar Population, and Dynamics of Extremely Metal-poor Galaxies (EMPGs): Are EMPGs Local Analogs of High-z Young Galaxies?*

Abstract We present the morphology and stellar population of 27 extremely metal-poor galaxies (EMPGs) at z ∼ 0 with metallicities of 0.01–0.1 Z ⊙. We conduct multicomponent surface brightness (SB) profile fitting for the deep Subaru/Hyper Suprime-Cam i-band images of the EMPGs with the Galfit software, carefully removing the SB contributions of tails. We find that the EMPGs with a median stellar mass of log ( M * / M ⊙ ) = 6.0 have a median Sérsic index of n = 1.1 and a median effective radius of r e = 200 pc, suggesting that typical EMPGs have a very compact disk. We compare the EMPGs with z ∼ 6 galaxies and local galaxies on the size–mass (r e –M *) diagram, and identify that the majority of the EMPGs have an r e –M * relation similar to z ∼ 0 star-forming galaxies rather than z ∼ 6 galaxies. Not every EMPG is a local analog of high-z young galaxies in the r e –M * relation. A spectrum of one pair of EMPG and tail, so far available, indicates that the tail is dynamically related to the EMPG with a median velocity difference of ΔV = 101 ± 32 km s−1. This moderately large ΔV cannot be explained by the dynamics of the tail, but likely by the infall on the tail. For the first time, we may identify the metal-poor star-forming system just now infalling into the tail.

Overconstrained models of time delay lenses redux: how the angular tail wags the radial dog

Abstract The two properties of the radial mass distribution of a gravitational lens that are well constrained by Einstein rings are the Einstein radius RE and ξ2 = REα″(RE)/(1 − κE), where α″(RE) and κE are the second derivative of the deflection profile and the convergence at RE, respectively. However, if there is a tight mathematical relationship between the radial mass profile and the angular structure, as is true of ellipsoids, an Einstein ring can appear to strongly distinguish radial mass distributions with the same ξ2. This problem is beautifully illustrated by the ellipsoidal models in Millon et al. When using Einstein rings to constrain the radial mass distribution, the angular structure of the models must contain all the degrees of freedom expected in nature (e.g. external shear, different ellipticities for the stars and the dark matter, modest deviations from elliptical structure, modest twists of the axes, modest ellipticity gradients, etc.) that work to decouple the radial and angular structures of the gravity. Models of Einstein rings with too few angular degrees of freedom will lead to strongly biased likelihood distinctions between radial mass distributions and very precise but inaccurate estimates of H0 based on gravitational lens time delays.

A Mini-Neptune and a Radius Valley Planet Orbiting the Nearby M2 Dwarf TOI-1266 in Its Venus Zone: Validation with the Habitable-zone Planet Finder

Abstract We report on the validation of two planets orbiting the nearby (36 pc) M2 dwarf TOI-1266 observed by the TESS mission. This system is one of a few M dwarf multiplanet systems with close-in planets where the inner planet is substantially larger than the outer planet. The inner planet is sub-Neptune-sized (R = 2.46 ± 0.08 R ⊕) with an orbital period of 10.9 days, while the outer planet has a radius of R ⊕ and resides in the exoplanet radius valley—the transition region between rocky and gaseous planets. With an orbital period of 18.8 days, the outer planet receives an insolation flux of 2.4 times that of Earth, similar to the insolation of Venus. Using precision near-infrared radial velocities with the Habitable-zone Planet Finder Spectrograph, we place upper mass limits of 15.9 and 6.4 M ⊕ at 95% confidence for the inner and outer planet, respectively. A more precise mass constraint of both planets, achievable with current radial velocity instruments given the host star brightness (V = 12.9, J = 9.7), will yield further insights into the dominant processes sculpting the exoplanet radius valley.

TOI-481 b and TOI-892 b: Two Long-period Hot Jupiters from the Transiting Exoplanet Survey Satellite

Abstract We present the discovery of two new 10 day period giant planets from the Transiting Exoplanet Survey Satellite mission, whose masses were precisely determined using a wide diversity of ground-based facilities. TOI-481 b and TOI-892 b have similar radii (0.99 ± 0.01 R J and 1.07 ± 0.02 R J , respectively), and orbital periods (10.3311 days and 10.6266 days, respectively), but significantly different masses (1.53 ± 0.03 M J versus 0.95 ± 0.07 M J , respectively). Both planets orbit metal-rich stars ( [ Fe / H ] = + 0.26 ± 0.05 dex and [ Fe / H ] = + 0.24 ± 0.05 for TOI-481 and TOI-892, respectively) but at different evolutionary stages. TOI-481 is a M ⋆ = 1.14 ± 0.02 M ⊙ , R ⋆ = 1.66 ± 0.02 R ⊙ G-type star ( T eff = 5735 ± 72 K), that with an age of 6.7 Gyr, is in the turn-off point of the main sequence. TOI-892 on the other hand, is a F-type dwarf star ( T eff = 6261 ± 80 K), which has a mass of M ⋆ = 1.28 ± 0.03 M ⊙ and a radius of R ⋆ = 1.39 ± 0.02 R ⊙ . TOI-481 b and TOI-892 b join the scarcely populated region of transiting gas giants with orbital periods longer than 10 days, which is important to constrain theories of the formation and structure of hot Jupiters.

Kilohertz quasi-periodic oscillations as probes of the X-ray color-color diagram and neutron star accretion-disk structure for Z sources

Based on the detected kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (NS-LMXBs), we investigate the evolution of the NS magnetosphere-disk structure along the Z track in the X-ray color-color diagram (CCD) for luminous Z sources, such as Cyg X-2, GX 5-1, GX 17+2, and Sco X-1. We find that the magnetosphere-disk radiusrinferred by kHz QPOs for all the sources shows a monotonically decreasing trend along the Z track from the horizontal branch (HB) to the normal branch (NB), implying that the dominated radiation components may dramatically change as the accretion disk moves toward the NS surface. In addition, the specific radius that corresponds to the HB/NB vertex is found to be aroundr ∼ 20 km, implying a potential characteristic position of transiting for the X-ray radiation mode. Furthermore, we find that the NBs that occur near the NS surface have a radius ofr ∼ 16−20 km, which is systematically smaller than those of HBs that have radii ofr ∼ 20−29 km. To interpret the relation between the CCD properties and the special magnetosphere-disk radii of Z sources, we suggest that the magnetic field lines corresponding to NB are “frozen-in” to the plasma, and move further inward with the shrinking of the NS magnetosphere-disk radius and pile up near the NS surface. They then form a strong magnetic field region aroundr ∼ 16−20 km, where the high magnetic energy density and high plasma mass density may dominate the radiation process in NB.

TOI-1728b: The Habitable-zone Planet Finder Confirms a Warm Super-Neptune Orbiting an M-dwarf Host

Abstract We confirm the planetary nature of TOI-1728b using a combination of ground-based photometry, near-infrared Doppler velocimetry and spectroscopy with the Habitable-zone Planet Finder. TOI-1728 is an old, inactive M0 star with T eff = K, which hosts a transiting super-Neptune at an orbital period of ∼3.49 days. Joint fitting of the radial velocities and TESS and ground-based transits yields a planetary radius of R ⊕, mass M ⊕, and eccentricity . We estimate the stellar properties, and perform a search for He 10830 Å absorption during the transit of this planet and claim a null detection with an upper limit of 1.1% with 90% confidence. A deeper level of He 10830 Å absorption has been detected in the planet atmosphere of GJ 3470b, a comparable gaseous planet. TOI-1728b is the largest super-Neptune—the intermediate subclass of planets between Neptune and the more massive gas-giant planets—discovered around an M dwarf. With its relatively large mass and radius, TOI-1728 represents a valuable data point in the M-dwarf exoplanet mass–radius diagram, bridging the gap between the lighter Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs. With a low bulk density of g cm−3, and orbiting a bright host star (J ∼ 9.6, V ∼ 12.4), TOI-1728b is also a promising candidate for transmission spectroscopy both from the ground and from space, which can be used to constrain planet formation and evolutionary models.

TESS Hunt for Young and Maturing Exoplanets (THYME). II. A 17 Myr Old Transiting Hot Jupiter in the Sco-Cen Association

Abstract We present the discovery of a transiting hot Jupiter orbiting HIP 67522 (T eff ∼ 5650 K; M * ∼ 1.2M ⊙) in the 10–20 Myr old Sco-Cen OB association. We identified the transits in the TESS data using our custom notch filter planet search pipeline and characterize the system with additional photometry from Spitzer; spectroscopy from SOAR/Goodman, SALT/HRS, LCOGT/NRES, and SMARTS/CHIRON; and speckle imaging from SOAR/HRCam. We model the photometry as a periodic Gaussian process with transits to account for stellar variability and find an orbital period of days and radius of R ⊕. We also identify a single transit of an additional candidate planet with radius R ⊕ that has an orbital period of ≳23 days. The validated planet HIP 67522b is currently the youngest transiting hot Jupiter discovered and is an ideal candidate for transmission spectroscopy and radial velocity follow-up studies, while also demonstrating that some young giant planets either form in situ at small orbital radii or else migrate promptly from formation sites farther out in the disk.

Overconstrained gravitational lens models and the Hubble constant

ABSTRACT It is well known that measurements of H0 from gravitational lens time delays scale as H0 ∝ 1 − κE, where κE is the mean convergence at the Einstein radius RE but that all available lens data other than the delays provide no direct constraints on κE. The properties of the radial mass distribution constrained by lens data are RE and the dimensionless quantity ξ = REα″(RE)/(1 − κE), where α″(RE) is the second derivative of the deflection profile at RE. Lens models with too few degrees of freedom, like power-law models with densities ρ ∝ r−n, have a one-to-one correspondence between ξ and κE (for a power-law model, ξ = 2(n − 2) and κE = (3 − n)/2 = (2 − ξ)/4). This means that highly constrained lens models with few parameters quickly lead to very precise but inaccurate estimates of κE and hence H0. Based on experiments with a broad range of plausible dark matter halo models, it is unlikely that any current estimates of H0 from gravitational lens time delays are more accurate than ${\sim} 10{{\ \rm per\ cent}}$, regardless of the reported precision.

New constraints on the structure of the nuclear stellar cluster of the Milky Way from star counts and MIR imaging

Context. The Milky Way nuclear star cluster (MWNSC) is a crucial laboratory for studying the galactic nuclei of other galaxies, but its properties have not been determined unambiguously until now. Aims. We aim to study the size and spatial structure of the MWNSC. Methods. This study uses data and methods that address potential shortcomings of previous studies on the topic. We use 0.2″ angular resolution Ks data to create a stellar density map in the central 86.4 pc × 21 pc at the Galactic center. We include data from selected adaptive-optics-assisted images obtained for the inner parsecs. In addition, we use Spitzer/IRAC mid-infrared (MIR) images. We model the Galactic bulge and the nuclear stellar disk in order to subtract them from the MWNSC. Finally, we fit a Sérsic model to the MWNSC and investigate its symmetry. Results. Our results are consistent with previous work. The MWNSC is flattened with an axis ratio of q = 0.71 ± 0.10, an effective radius of Re = (5.1 ± 1.0) pc, and a Sérsic index of n = 2.2 ± 0.7. Its major axis may be tilted out of the Galactic plane by up to −10°. The distribution of the giants brighter than the Red Clump (RC) is found to be significantly flatter than the distribution of the faint stars. We investigate the 3D structure of the central stellar cusp using our results on the MWNSC structure on large scales to constrain the deprojection of the measured stellar surface number density, obtaining a value of the 3D inner power law of γ = 1.38 ± 0.06sys ± 0.01stat. Conclusions. The MWNSC shares its main properties with other extragalactic NSCs found in spiral galaxies. The differences in the structure between bright giants and RC stars might be related to the existence of not completely mixed populations of different ages. This may hint at recent growth of the MWNSC through star formation or cluster accretion.

TESS Discovery of an Ultra-short-period Planet around the Nearby M Dwarf LHS 3844

Abstract Data from the newly commissioned Transiting Exoplanet Survey Satellite has revealed a “hot Earth” around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of R ⊕ and orbits the star every 11 hr. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough (I = 11.9, K = 9.1) for this possibility to be investigated with transit and occultation spectroscopy. The star’s brightness and the planet’s short period will also facilitate the measurement of the planet’s mass through Doppler spectroscopy.

The analysis of effective galaxies number count for Chinese Space Station Optical Survey (CSS-OS) by image simulation

The Chinese Space Station Optical Survey (CSS-OS) is a mission to explore the vast universe. This mission will equip a 2-meter space telescope to perform a multi-band NUV-optical large area survey (over 40% of the sky) and deep survey (~1% of the sky) for the cosmological and astronomical goals. Galaxy detection is one of the most important methods to achieve scientific goals. In this paper, we evaluate the galaxy number density for CSS-OS in i band (depth, i ~26 for large area survey and ~27 for the deep survey, point source, 5-sigma by the method of image simulation. We also compare galaxies detected by CSS-OS with that of LSST (i~27, point source, 5-sigma. In our simulation, the HUDF galaxy catalogs are used to create mock images due to long enough integration time which meets the completeness requirements of the galaxy analysis for CSS-OS and LSST. The galaxy surface profile and spectrum are produced by the morphological information, photometric redshift and SEDs from the catalogs. The instrumental features and the environmental condition are also considered to produce the mock galaxy images. The galaxies of CSS-OS and LSST are both extracted by SExtractor from the mock i band image and matched with the original catalog. Through the analysis of the extracted galaxies, we find that the effective galaxy number count is ~13 arcmin^-2, ~40 arcmin^-2 and ~42 arcmin^-2 for CSS-OS large area survey, CSS-OS deep survey and LSST, respectively. Moreover, CSS-OS shows the advantage in small galaxy detection with high spatial resolution, especially for the deep survey: about 20% of the galaxies detected by CSS-OS deep survey are not detected by LSST, and they have a small effective radius of re < 0.3".

An Enigmatic Population of Luminous Globular Clusters in a Galaxy Lacking Dark Matter

Abstract We recently found an ultra diffuse galaxy (UDG) with a half-light radius of R e = 2.2 kpc and little or no dark matter. The total mass of NGC1052–DF2 was measured from the radial velocities of bright compact objects that are associated with the galaxy. Here, we analyze these objects using a combination of Hubble Space Telescope (HST) imaging and Keck spectroscopy. Their average size is pc and their average ellipticity is . From a stacked Keck spectrum we derive an age of ≳9 Gyr and a metallicity of [Fe/H] = −1.35 ± 0.12. Their properties are similar to ω Centauri, the brightest and largest globular cluster in the Milky Way, and our results demonstrate that the luminosity function of metal-poor globular clusters is not universal. The fraction of the total stellar mass that is in the globular cluster system is similar to that in other UDGs, and consistent with “failed galaxy” scenarios, where star formation terminated shortly after the clusters were formed. However, the galaxy is a factor of ∼1000 removed from the relation between globular cluster mass and total galaxy mass that has been found for other galaxies, including other UDGs. We infer that a dark matter halo is not a prerequisite for the formation of metal-poor globular cluster-like objects in high-redshift galaxies.