TY - JOUR
T1 - Subaru mid-infrared imaging of the quadruple lenses. II. unveiling lens structure of MG0414+0534 and Q2237+030
AU - Minezaki, Takeo
AU - Chiba, Masashi
AU - Kashikawa, Nobunari
AU - Inoue, Kaiki Taro
AU - Kataza, Hirokazu
PY - 2009
Y1 - 2009
N2 - We present mid-infrared imaging at 11.7 μm for the quadruple lens systems, MG0414+0534 and Q2237+030, using the cooled mid-infrared camera and spectrometer attached on the Subaru telescope. MG0414+0534 is characterized by a bright pair of lensed images (A1, A2) and their optical flux ratio A2/A1 deviates significantly from the prediction of a smooth-lens model. Q2237+030 is "the Einstein Cross" being comprised of four lensed images, which are significantly affected by microlensing in a foreground lensing galaxy. Our mid-infrared observations of these lensed images have revealed that the mid-infrared flux ratio for A2/A1 of MG0414+0534 is nearly unity (0.90 0.04). We find that this flux ratio is systematically small, at 4-5σ level, compared with the prediction of a best smooth-lens model (1.09) represented by a singular isothermal ellipsoid and external shear. The smooth-lens model, which also considers the additional lensing effect of the possible faint satellite, object X, still provides a large flux ratio of A2/A1=1.06, thereby suggesting the presence of more substructures that can explain our observational result. In contrast, for Q2237+030, our high signal-to-noise observation indicates that the mid-infrared flux ratios between all the four images of Q2237+030 are virtually consistent with the prediction of a smooth-lens model. Based on the size estimate of the dust torus surrounding the nuclei of these QSOs, we set limits on the mass of a substructure in these lens systems, which can cause anomalies in the flux ratios. For MG0414+0534, since the required mass of a substructure inside its Einstein radius is ≳360 M ⊙, millilensing by a cold dark matter substructure is most likely. If it is modeled as a singular isothermal sphere, the mass inside a radius of 100 pc is given as ≳1.0 × 105 M ⊙. For Q2237+030, there is no significant evidence of millilensing, so the reported anomalous flux ratios in shorter wavelengths are entirely caused due to microlensing by stars.
AB - We present mid-infrared imaging at 11.7 μm for the quadruple lens systems, MG0414+0534 and Q2237+030, using the cooled mid-infrared camera and spectrometer attached on the Subaru telescope. MG0414+0534 is characterized by a bright pair of lensed images (A1, A2) and their optical flux ratio A2/A1 deviates significantly from the prediction of a smooth-lens model. Q2237+030 is "the Einstein Cross" being comprised of four lensed images, which are significantly affected by microlensing in a foreground lensing galaxy. Our mid-infrared observations of these lensed images have revealed that the mid-infrared flux ratio for A2/A1 of MG0414+0534 is nearly unity (0.90 0.04). We find that this flux ratio is systematically small, at 4-5σ level, compared with the prediction of a best smooth-lens model (1.09) represented by a singular isothermal ellipsoid and external shear. The smooth-lens model, which also considers the additional lensing effect of the possible faint satellite, object X, still provides a large flux ratio of A2/A1=1.06, thereby suggesting the presence of more substructures that can explain our observational result. In contrast, for Q2237+030, our high signal-to-noise observation indicates that the mid-infrared flux ratios between all the four images of Q2237+030 are virtually consistent with the prediction of a smooth-lens model. Based on the size estimate of the dust torus surrounding the nuclei of these QSOs, we set limits on the mass of a substructure in these lens systems, which can cause anomalies in the flux ratios. For MG0414+0534, since the required mass of a substructure inside its Einstein radius is ≳360 M ⊙, millilensing by a cold dark matter substructure is most likely. If it is modeled as a singular isothermal sphere, the mass inside a radius of 100 pc is given as ≳1.0 × 105 M ⊙. For Q2237+030, there is no significant evidence of millilensing, so the reported anomalous flux ratios in shorter wavelengths are entirely caused due to microlensing by stars.
KW - Gravitational lensing
KW - Infrared: galaxies
UR - http://www.scopus.com/inward/record.url?scp=66649107779&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=66649107779&partnerID=8YFLogxK
U2 - 10.1088/0004-637X/697/1/610
DO - 10.1088/0004-637X/697/1/610
M3 - Article
AN - SCOPUS:66649107779
VL - 697
SP - 610
EP - 618
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
ER -